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 $48.28   13.321%   $54.7114   $54.71   $54.70   $54.70  
  Purchase #2 $129.92   11.661%   $145.07   $145.07   $145.05   $145.10  
  Purchase #3 $177.77   9.122%   $193.9862   $193.99   $194.00   $194.00  
  Purchase #4 $120.51   10.358%   $132.9924   $132.99   $133.00   $133.00  
  Purchase #5 $69.26   9.609%   $75.9152   $75.92   $75.90   $75.90  
  Purchase #6 $159.59   13.843%   $181.682   $181.68   $181.70   $181.70  
  Purchase #7 $33.50   10.388%   $36.98   $36.98   $37.00   $37.00  
  7 purchase totals = $738.83       $821.3372   $821.34   $821.35   $821.40