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 $59.72   4.145%   $62.1954   $62.20   $62.20   $62.20  
  Purchase #2 $210.61   3.246%   $217.4464   $217.45   $217.45   $217.40  
  Purchase #3 $166.75   4.131%   $173.6384   $173.64   $173.65   $173.60  
  Purchase #4 $94.81   8.315%   $102.6935   $102.69   $102.70   $102.70  
  Purchase #5 $155.93   3.241%   $160.9837   $160.98   $161.00   $161.00  
  Purchase #6 $23.79   3.131%   $24.5349   $24.53   $24.55   $24.50  
  Purchase #7 $228.67   4.264%   $238.4205   $238.42   $238.40   $238.40  
  7 purchase totals = $940.28       $979.9128   $979.91   $979.95   $979.80