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 $215.83   5.156%   $226.9582   $226.96   $226.95   $227.00  
  Purchase #2 $219.67   7.792%   $236.7867   $236.79   $236.80   $236.80  
  Purchase #3 $226.61   8.580%   $246.0531   $246.05   $246.05   $246.10  
  Purchase #4 $20.93   8.754%   $22.7622   $22.76   $22.75   $22.80  
  Purchase #5 $133.26   11.645%   $148.7781   $148.78   $148.80   $148.80  
  Purchase #6 $23.75   12.204%   $26.6485   $26.65   $26.65   $26.60  
  Purchase #7 $67.51   11.120%   $75.0171   $75.02   $75.00   $75.00  
  7 purchase totals = $907.56       $983.0039   $983.01   $983.00   $983.10