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 $72.59   13.743%   $82.566   $82.57   $82.55   $82.60  
  Purchase #2 $56.95   3.202%   $58.7735   $58.77   $58.75   $58.80  
  Purchase #3 $236.36   7.519%   $254.1319   $254.13   $254.15   $254.10  
  Purchase #4 $94.53   8.605%   $102.6643   $102.66   $102.65   $102.70  
  Purchase #5 $161.48   3.665%   $167.3982   $167.40   $167.40   $167.40  
  Purchase #6 $91.43   13.787%   $104.0355   $104.04   $104.05   $104.00  
  Purchase #7 $75.65   10.234%   $83.392   $83.39   $83.40   $83.40  
  7 purchase totals = $788.99       $852.9614   $852.96   $852.95   $853.00