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 $61.51   7.719%   $66.258   $66.26   $66.25   $66.30  
  Purchase #2 $72.89   10.670%   $80.6674   $80.67   $80.65   $80.70  
  Purchase #3 $170.85   5.107%   $179.5753   $179.58   $179.60   $179.60  
  Purchase #4 $14.56   13.391%   $16.5097   $16.51   $16.50   $16.50  
  Purchase #5 $144.52   5.265%   $152.129   $152.13   $152.15   $152.10  
  Purchase #6 $237.46   8.788%   $258.328   $258.33   $258.35   $258.30  
  Purchase #7 $204.67   13.533%   $232.368   $232.37   $232.35   $232.40  
  7 purchase totals = $906.46       $985.8354   $985.85   $985.85   $985.90