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 $156.65   3.192%   $161.6503   $161.65   $161.65   $161.70  
  Purchase #2 $230.56   12.650%   $259.7258   $259.73   $259.75   $259.70  
  Purchase #3 $54.66   6.604%   $58.2697   $58.27   $58.25   $58.30  
  Purchase #4 $225.95   9.321%   $247.0108   $247.01   $247.00   $247.00  
  Purchase #5 $108.35   9.243%   $118.3648   $118.36   $118.35   $118.40  
  Purchase #6 $162.26   4.466%   $169.5065   $169.51   $169.50   $169.50  
  Purchase #7 $15.91   12.634%   $17.9201   $17.92   $17.90   $17.90  
  7 purchase totals = $954.34       $1,032.4480   $1,032.45   $1,032.40   $1,032.50