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 $49.84   5.353%   $52.5079   $52.51   $52.50   $52.50  
  Purchase #2 $87.67   9.123%   $95.6681   $95.67   $95.65   $95.70  
  Purchase #3 $52.26   9.846%   $57.4055   $57.41   $57.40   $57.40  
  Purchase #4 $220.49   3.818%   $228.9083   $228.91   $228.90   $228.90  
  Purchase #5 $162.79   5.770%   $172.183   $172.18   $172.20   $172.20  
  Purchase #6 $13.48   9.702%   $14.7878   $14.79   $14.80   $14.80  
  Purchase #7 $124.47   13.206%   $140.9075   $140.91   $140.90   $140.90  
  7 purchase totals = $711.00       $762.3681   $762.38   $762.35   $762.40