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 $176.96   4.117%   $184.2454   $184.25   $184.25   $184.20  
  Purchase #2 $179.65   7.660%   $193.4112   $193.41   $193.40   $193.40  
  Purchase #3 $113.44   12.262%   $127.35   $127.35   $127.35   $127.40  
  Purchase #4 $104.71   13.687%   $119.0417   $119.04   $119.05   $119.00  
  Purchase #5 $91.35   5.492%   $96.3669   $96.37   $96.35   $96.40  
  Purchase #6 $43.67   8.622%   $47.4352   $47.44   $47.45   $47.40  
  Purchase #7 $231.46   6.251%   $245.9286   $245.93   $245.95   $245.90  
  7 purchase totals = $941.24       $1,013.7790   $1,013.79   $1,013.80   $1,013.70