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 $53.82   11.727%   $60.1315   $60.13   $60.15   $60.10  
  Purchase #2 $185.98   4.159%   $193.7149   $193.71   $193.70   $193.70  
  Purchase #3 $27.79   3.459%   $28.7513   $28.75   $28.75   $28.80  
  Purchase #4 $112.26   12.663%   $126.4755   $126.48   $126.50   $126.50  
  Purchase #5 $167.78   3.280%   $173.2832   $173.28   $173.30   $173.30  
  Purchase #6 $26.32   7.184%   $28.2108   $28.21   $28.20   $28.20  
  Purchase #7 $37.79   4.861%   $39.627   $39.63   $39.65   $39.60  
  7 purchase totals = $611.74       $650.1942   $650.19   $650.25   $650.20