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 $206.91   10.682%   $229.0121   $229.01   $229.00   $229.00  
  Purchase #2 $136.74   9.286%   $149.4377   $149.44   $149.45   $149.40  
  Purchase #3 $179.44   8.507%   $194.705   $194.71   $194.70   $194.70  
  Purchase #4 $203.45   3.543%   $210.6582   $210.66   $210.65   $210.70  
  Purchase #5 $54.74   6.220%   $58.1448   $58.14   $58.15   $58.10  
  Purchase #6 $188.44   12.776%   $212.5151   $212.52   $212.50   $212.50  
  Purchase #7 $148.58   4.427%   $155.1576   $155.16   $155.15   $155.20  
  7 purchase totals = $1,118.30       $1,209.6305   $1,209.64   $1,209.60   $1,209.60