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 $211.47   13.769%   $240.5873   $240.59   $240.60   $240.60  
  Purchase #2 $235.56   13.773%   $268.0037   $268.00   $268.00   $268.00  
  Purchase #3 $73.80   11.521%   $82.3025   $82.30   $82.30   $82.30  
  Purchase #4 $11.58   7.266%   $12.4214   $12.42   $12.40   $12.40  
  Purchase #5 $29.90   8.753%   $32.5171   $32.52   $32.50   $32.50  
  Purchase #6 $16.30   7.695%   $17.5543   $17.55   $17.55   $17.60  
  Purchase #7 $183.90   10.237%   $202.7258   $202.73   $202.75   $202.70  
  7 purchase totals = $762.51       $856.1121   $856.11   $856.10   $856.10