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 $167.48   13.781%   $190.5604   $190.56   $190.55   $190.60  
  Purchase #2 $68.56   10.814%   $75.9741   $75.97   $75.95   $76.00  
  Purchase #3 $98.90   11.824%   $110.5939   $110.59   $110.60   $110.60  
  Purchase #4 $154.55   3.772%   $160.3796   $160.38   $160.40   $160.40  
  Purchase #5 $123.56   6.630%   $131.752   $131.75   $131.75   $131.80  
  Purchase #6 $161.91   12.474%   $182.1067   $182.11   $182.10   $182.10  
  Purchase #7 $53.43   6.192%   $56.7384   $56.74   $56.75   $56.70  
  7 purchase totals = $828.39       $908.1051   $908.10   $908.10   $908.20