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 $60.93   6.717%   $65.0227   $65.02   $65.00   $65.00  
  Purchase #2 $230.35   4.800%   $241.4068   $241.41   $241.40   $241.40  
  Purchase #3 $73.35   3.464%   $75.8908   $75.89   $75.90   $75.90  
  Purchase #4 $6.88   5.545%   $7.2615   $7.26   $7.25   $7.30  
  Purchase #5 $186.66   10.488%   $206.2369   $206.24   $206.25   $206.20  
  Purchase #6 $30.91   11.687%   $34.5225   $34.52   $34.50   $34.50  
  Purchase #7 $170.68   6.511%   $181.793   $181.79   $181.80   $181.80  
  7 purchase totals = $759.76       $812.1342   $812.13   $812.10   $812.10