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 $186.56   4.539%   $195.028   $195.03   $195.05   $195.00  
  Purchase #2 $98.76   13.419%   $112.0126   $112.01   $112.00   $112.00  
  Purchase #3 $9.38   3.491%   $9.7075   $9.71   $9.70   $9.70  
  Purchase #4 $197.84   3.276%   $204.3212   $204.32   $204.30   $204.30  
  Purchase #5 $220.85   4.307%   $230.362   $230.36   $230.35   $230.40  
  Purchase #6 $102.82   4.648%   $107.5991   $107.60   $107.60   $107.60  
  Purchase #7 $144.61   13.547%   $164.2003   $164.20   $164.20   $164.20  
  7 purchase totals = $960.82       $1,023.2307   $1,023.23   $1,023.20   $1,023.20