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 $62.33   3.122%   $64.2759   $64.28   $64.30   $64.30  
  Purchase #2 $135.81   7.728%   $146.3054   $146.31   $146.30   $146.30  
  Purchase #3 $118.78   13.222%   $134.4851   $134.49   $134.50   $134.50  
  Purchase #4 $10.51   3.653%   $10.8939   $10.89   $10.90   $10.90  
  Purchase #5 $180.65   10.869%   $200.2848   $200.28   $200.30   $200.30  
  Purchase #6 $5.97   3.462%   $6.1767   $6.18   $6.20   $6.20  
  Purchase #7 $198.85   11.104%   $220.9303   $220.93   $220.95   $220.90  
  7 purchase totals = $712.90       $783.3521   $783.36   $783.45   $783.40