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 $63.83   3.241%   $65.8987   $65.90   $65.90   $65.90  
  Purchase #2 $167.53   5.408%   $176.59   $176.59   $176.60   $176.60  
  Purchase #3 $23.58   6.375%   $25.0832   $25.08   $25.10   $25.10  
  Purchase #4 $187.35   6.507%   $199.5409   $199.54   $199.55   $199.50  
  Purchase #5 $47.53   8.600%   $51.6176   $51.62   $51.60   $51.60  
  Purchase #6 $234.65   13.250%   $265.7411   $265.74   $265.75   $265.70  
  Purchase #7 $182.25   11.439%   $203.0976   $203.10   $203.10   $203.10  
  7 purchase totals = $906.72       $987.5691   $987.57   $987.60   $987.50