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 $76.67   11.209%   $85.2639   $85.26   $85.25   $85.30  
  Purchase #2 $38.97   11.378%   $43.404   $43.40   $43.40   $43.40  
  Purchase #3 $56.53   7.515%   $60.7782   $60.78   $60.80   $60.80  
  Purchase #4 $229.74   11.136%   $255.3238   $255.32   $255.30   $255.30  
  Purchase #5 $170.57   5.396%   $179.774   $179.77   $179.75   $179.80  
  Purchase #6 $208.46   11.450%   $232.3287   $232.33   $232.35   $232.30  
  Purchase #7 $50.69   7.263%   $54.3716   $54.37   $54.35   $54.40  
  7 purchase totals = $831.63       $911.2442   $911.23   $911.20   $911.30