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 $69.50   8.304%   $75.2713   $75.27   $75.25   $75.30  
  Purchase #2 $25.26   5.393%   $26.6223   $26.62   $26.60   $26.60  
  Purchase #3 $55.60   5.532%   $58.6758   $58.68   $58.70   $58.70  
  Purchase #4 $121.69   3.152%   $125.5257   $125.53   $125.55   $125.50  
  Purchase #5 $205.43   10.413%   $226.8214   $226.82   $226.80   $226.80  
  Purchase #6 $83.71   10.160%   $92.2149   $92.21   $92.20   $92.20  
  Purchase #7 $160.29   10.416%   $176.9858   $176.99   $177.00   $177.00  
  7 purchase totals = $721.48       $782.1172   $782.12   $782.10   $782.10