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 $57.81   11.702%   $64.5749   $64.57   $64.55   $64.60  
  Purchase #2 $213.77   13.779%   $243.2254   $243.23   $243.25   $243.20  
  Purchase #3 $160.45   13.152%   $181.5524   $181.55   $181.55   $181.60  
  Purchase #4 $234.33   6.462%   $249.4724   $249.47   $249.45   $249.50  
  Purchase #5 $185.87   8.217%   $201.1429   $201.14   $201.15   $201.10  
  Purchase #6 $191.49   13.447%   $217.2397   $217.24   $217.25   $217.20  
  Purchase #7 $80.36   8.843%   $87.4662   $87.47   $87.45   $87.50  
  7 purchase totals = $1,124.08       $1,244.6739   $1,244.67   $1,244.65   $1,244.70