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 $188.45   8.406%   $204.2911   $204.29   $204.30   $204.30  
  Purchase #2 $247.29   5.159%   $260.0477   $260.05   $260.05   $260.00  
  Purchase #3 $10.79   8.669%   $11.7254   $11.73   $11.75   $11.70  
  Purchase #4 $69.40   13.269%   $78.6087   $78.61   $78.60   $78.60  
  Purchase #5 $236.59   11.435%   $263.6441   $263.64   $263.65   $263.60  
  Purchase #6 $142.34   7.245%   $152.6525   $152.65   $152.65   $152.70  
  Purchase #7 $23.80   7.419%   $25.5657   $25.57   $25.55   $25.60  
  7 purchase totals = $918.66       $996.5352   $996.54   $996.55   $996.50