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 $118.42   13.651%   $134.5855   $134.59   $134.60   $134.60  
  Purchase #2 $127.68   12.467%   $143.5979   $143.60   $143.60   $143.60  
  Purchase #3 $243.62   6.340%   $259.0655   $259.07   $259.05   $259.10  
  Purchase #4 $68.39   6.353%   $72.7348   $72.73   $72.75   $72.70  
  Purchase #5 $97.78   10.306%   $107.8572   $107.86   $107.85   $107.90  
  Purchase #6 $23.77   8.853%   $25.8744   $25.87   $25.85   $25.90  
  Purchase #7 $97.58   10.405%   $107.7332   $107.73   $107.75   $107.70  
  7 purchase totals = $777.24       $851.4485   $851.45   $851.45   $851.50