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 $69.57   8.306%   $75.3485   $75.35   $75.35   $75.30  
  Purchase #2 $217.27   9.269%   $237.4088   $237.41   $237.40   $237.40  
  Purchase #3 $50.53   8.364%   $54.7563   $54.76   $54.75   $54.80  
  Purchase #4 $163.82   6.144%   $173.8851   $173.89   $173.90   $173.90  
  Purchase #5 $44.34   12.364%   $49.8222   $49.82   $49.80   $49.80  
  Purchase #6 $10.90   11.542%   $12.1581   $12.16   $12.15   $12.20  
  Purchase #7 $202.78   8.534%   $220.0852   $220.09   $220.10   $220.10  
  7 purchase totals = $759.21       $823.4642   $823.48   $823.45   $823.50