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 $67.99   5.119%   $71.4704   $71.47   $71.45   $71.50  
  Purchase #2 $157.70   4.566%   $164.9006   $164.90   $164.90   $164.90  
  Purchase #3 $194.38   3.753%   $201.6751   $201.68   $201.70   $201.70  
  Purchase #4 $24.45   5.486%   $25.7913   $25.79   $25.80   $25.80  
  Purchase #5 $71.71   4.385%   $74.8545   $74.85   $74.85   $74.90  
  Purchase #6 $59.63   10.259%   $65.7474   $65.75   $65.75   $65.70  
  Purchase #7 $43.61   5.475%   $45.9976   $46.00   $46.00   $46.00  
  7 purchase totals = $619.47       $650.4369   $650.44   $650.45   $650.50