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 $66.54   11.213%   $74.0011   $74.00   $74.00   $74.00  
  Purchase #2 $100.97   6.751%   $107.7865   $107.79   $107.80   $107.80  
  Purchase #3 $206.43   4.346%   $215.4014   $215.40   $215.40   $215.40  
  Purchase #4 $157.59   12.165%   $176.7608   $176.76   $176.75   $176.80  
  Purchase #5 $98.35   3.289%   $101.5847   $101.58   $101.60   $101.60  
  Purchase #6 $109.41   12.436%   $123.0162   $123.02   $123.00   $123.00  
  Purchase #7 $52.39   12.386%   $58.879   $58.88   $58.90   $58.90  
  7 purchase totals = $791.68       $857.4297   $857.43   $857.45   $857.50