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 $19.88   8.360%   $21.542   $21.54   $21.55   $21.50  
  Purchase #2 $220.31   5.519%   $232.4689   $232.47   $232.45   $232.50  
  Purchase #3 $193.61   5.427%   $204.1172   $204.12   $204.10   $204.10  
  Purchase #4 $78.31   11.857%   $87.5952   $87.60   $87.60   $87.60  
  Purchase #5 $202.28   4.689%   $211.7649   $211.76   $211.75   $211.80  
  Purchase #6 $102.56   6.137%   $108.8541   $108.85   $108.85   $108.90  
  Purchase #7 $205.50   7.591%   $221.0995   $221.10   $221.10   $221.10  
  7 purchase totals = $1,022.45       $1,087.4418   $1,087.44   $1,087.40   $1,087.50