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 $116.66   12.561%   $131.3137   $131.31   $131.30   $131.30  
  Purchase #2 $211.46   8.436%   $229.2988   $229.30   $229.30   $229.30  
  Purchase #3 $171.50   8.359%   $185.8357   $185.84   $185.85   $185.80  
  Purchase #4 $235.94   4.780%   $247.2179   $247.22   $247.20   $247.20  
  Purchase #5 $138.78   11.408%   $154.612   $154.61   $154.60   $154.60  
  Purchase #6 $26.30   12.735%   $29.6493   $29.65   $29.65   $29.60  
  Purchase #7 $236.89   4.158%   $246.7399   $246.74   $246.75   $246.70  
  7 purchase totals = $1,137.53       $1,224.6673   $1,224.67   $1,224.65   $1,224.50