Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $103.61   13.416%   $117.5103   $117.51   $117.50   $117.50  
  Purchase #2 $192.46   12.572%   $216.6561   $216.66   $216.65   $216.70  
  Purchase #3 $170.76   11.221%   $189.921   $189.92   $189.90   $189.90  
  Purchase #4 $233.31   12.375%   $262.1821   $262.18   $262.20   $262.20  
  Purchase #5 $145.51   5.472%   $153.4723   $153.47   $153.45   $153.50  
  Purchase #6 $116.70   4.526%   $121.9818   $121.98   $122.00   $122.00  
  Purchase #7 $225.59   9.430%   $246.8631   $246.86   $246.85   $246.90  
  7 purchase totals = $1,187.94       $1,308.5867   $1,308.58   $1,308.55   $1,308.70