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 $206.76   13.345%   $234.3521   $234.35   $234.35   $234.40  
  Purchase #2 $101.43   8.402%   $109.9521   $109.95   $109.95   $110.00  
  Purchase #3 $121.44   10.756%   $134.5021   $134.50   $134.50   $134.50  
  Purchase #4 $125.45   3.558%   $129.9135   $129.91   $129.90   $129.90  
  Purchase #5 $65.48   11.715%   $73.151   $73.15   $73.15   $73.20  
  Purchase #6 $196.79   13.377%   $223.1146   $223.11   $223.10   $223.10  
  Purchase #7 $231.38   6.387%   $246.1582   $246.16   $246.15   $246.20  
  7 purchase totals = $1,048.73       $1,151.1436   $1,151.13   $1,151.10   $1,151.30