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 $184.77   12.854%   $208.5203   $208.52   $208.50   $208.50  
  Purchase #2 $150.95   10.207%   $166.3575   $166.36   $166.35   $166.40  
  Purchase #3 $67.42   8.312%   $73.024   $73.02   $73.00   $73.00  
  Purchase #4 $67.88   3.216%   $70.063   $70.06   $70.05   $70.10  
  Purchase #5 $193.69   5.453%   $204.2519   $204.25   $204.25   $204.30  
  Purchase #6 $102.68   3.854%   $106.6373   $106.64   $106.65   $106.60  
  Purchase #7 $173.43   12.741%   $195.5267   $195.53   $195.55   $195.50  
  7 purchase totals = $940.82       $1,024.3807   $1,024.38   $1,024.35   $1,024.40