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 $179.52   13.695%   $204.1053   $204.11   $204.10   $204.10  
  Purchase #2 $182.69   13.109%   $206.6388   $206.64   $206.65   $206.60  
  Purchase #3 $23.38   9.196%   $25.53   $25.53   $25.55   $25.50  
  Purchase #4 $76.77   10.125%   $84.543   $84.54   $84.55   $84.50  
  Purchase #5 $234.38   8.832%   $255.0804   $255.08   $255.10   $255.10  
  Purchase #6 $92.90   5.451%   $97.964   $97.96   $97.95   $98.00  
  Purchase #7 $170.72   11.536%   $190.4143   $190.41   $190.40   $190.40  
  7 purchase totals = $960.36       $1,064.2758   $1,064.27   $1,064.30   $1,064.20