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 $72.62   12.451%   $81.6619   $81.66   $81.65   $81.70  
  Purchase #2 $180.99   12.531%   $203.6699   $203.67   $203.65   $203.70  
  Purchase #3 $165.92   5.759%   $175.4753   $175.48   $175.50   $175.50  
  Purchase #4 $179.54   5.737%   $189.8402   $189.84   $189.85   $189.80  
  Purchase #5 $178.98   8.607%   $194.3848   $194.38   $194.40   $194.40  
  Purchase #6 $120.92   11.681%   $135.0447   $135.04   $135.05   $135.00  
  Purchase #7 $202.93   10.518%   $224.2742   $224.27   $224.25   $224.30  
  7 purchase totals = $1,101.90       $1,204.3510   $1,204.34   $1,204.35   $1,204.40