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 $212.72   10.383%   $234.8067   $234.81   $234.80   $234.80  
  Purchase #2 $228.34   8.114%   $246.8675   $246.87   $246.85   $246.90  
  Purchase #3 $68.96   5.545%   $72.7838   $72.78   $72.80   $72.80  
  Purchase #4 $145.82   12.643%   $164.256   $164.26   $164.25   $164.30  
  Purchase #5 $224.98   12.716%   $253.5885   $253.59   $253.60   $253.60  
  Purchase #6 $160.68   6.196%   $170.6357   $170.64   $170.65   $170.60  
  Purchase #7 $202.33   5.604%   $213.6686   $213.67   $213.65   $213.70  
  7 purchase totals = $1,243.83       $1,356.6068   $1,356.62   $1,356.60   $1,356.70