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 $73.35   7.267%   $78.6803   $78.68   $78.70   $78.70  
  Purchase #2 $152.94   9.414%   $167.3378   $167.34   $167.35   $167.30  
  Purchase #3 $112.31   5.596%   $118.5949   $118.59   $118.60   $118.60  
  Purchase #4 $79.97   6.179%   $84.9113   $84.91   $84.90   $84.90  
  Purchase #5 $219.45   9.747%   $240.8398   $240.84   $240.85   $240.80  
  Purchase #6 $89.53   4.187%   $93.2786   $93.28   $93.30   $93.30  
  Purchase #7 $84.29   12.714%   $95.0066   $95.01   $95.00   $95.00  
  7 purchase totals = $811.84       $878.6493   $878.65   $878.70   $878.60