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 $210.39   10.713%   $232.9291   $232.93   $232.95   $232.90  
  Purchase #2 $5.60   11.523%   $6.2453   $6.25   $6.25   $6.20  
  Purchase #3 $199.29   11.268%   $221.746   $221.75   $221.75   $221.70  
  Purchase #4 $102.33   4.378%   $106.81   $106.81   $106.80   $106.80  
  Purchase #5 $146.27   11.259%   $162.7385   $162.74   $162.75   $162.70  
  Purchase #6 $25.33   11.791%   $28.3167   $28.32   $28.30   $28.30  
  Purchase #7 $244.55   4.254%   $254.9532   $254.95   $254.95   $255.00  
  7 purchase totals = $933.76       $1,013.7388   $1,013.75   $1,013.75   $1,013.60