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 $180.71   9.696%   $198.2316   $198.23   $198.25   $198.20  
  Purchase #2 $121.61   8.323%   $131.7316   $131.73   $131.75   $131.70  
  Purchase #3 $29.94   10.442%   $33.0663   $33.07   $33.05   $33.10  
  Purchase #4 $109.66   13.201%   $124.1362   $124.14   $124.15   $124.10  
  Purchase #5 $61.81   11.305%   $68.7976   $68.80   $68.80   $68.80  
  Purchase #6 $246.44   4.133%   $256.6254   $256.63   $256.65   $256.60  
  Purchase #7 $209.40   11.840%   $234.193   $234.19   $234.20   $234.20  
  7 purchase totals = $959.57       $1,046.7817   $1,046.79   $1,046.85   $1,046.70