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 $56.30   11.492%   $62.77   $62.77   $62.75   $62.80  
  Purchase #2 $110.98   12.444%   $124.7904   $124.79   $124.80   $124.80  
  Purchase #3 $22.34   11.582%   $24.9274   $24.93   $24.95   $24.90  
  Purchase #4 $244.93   9.738%   $268.7813   $268.78   $268.80   $268.80  
  Purchase #5 $81.55   4.365%   $85.1097   $85.11   $85.10   $85.10  
  Purchase #6 $131.37   4.207%   $136.8967   $136.90   $136.90   $136.90  
  Purchase #7 $58.26   8.757%   $63.3618   $63.36   $63.35   $63.40  
  7 purchase totals = $705.73       $766.6373   $766.64   $766.65   $766.70