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 $169.46   10.166%   $186.6873   $186.69   $186.70   $186.70  
  Purchase #2 $53.71   11.229%   $59.7411   $59.74   $59.75   $59.70  
  Purchase #3 $61.53   11.186%   $68.4127   $68.41   $68.40   $68.40  
  Purchase #4 $170.64   6.693%   $182.0609   $182.06   $182.05   $182.10  
  Purchase #5 $182.31   10.678%   $201.7771   $201.78   $201.80   $201.80  
  Purchase #6 $85.43   8.648%   $92.818   $92.82   $92.80   $92.80  
  Purchase #7 $212.94   7.668%   $229.2682   $229.27   $229.25   $229.30  
  7 purchase totals = $936.02       $1,020.7653   $1,020.77   $1,020.75   $1,020.80