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 $226.98   6.213%   $241.0823   $241.08   $241.10   $241.10  
  Purchase #2 $66.99   4.776%   $70.1894   $70.19   $70.20   $70.20  
  Purchase #3 $10.68   13.361%   $12.107   $12.11   $12.10   $12.10  
  Purchase #4 $110.54   8.464%   $119.8961   $119.90   $119.90   $119.90  
  Purchase #5 $198.76   5.845%   $210.3775   $210.38   $210.40   $210.40  
  Purchase #6 $146.52   8.277%   $158.6475   $158.65   $158.65   $158.60  
  Purchase #7 $153.59   6.639%   $163.7868   $163.79   $163.80   $163.80  
  7 purchase totals = $914.06       $976.0866   $976.10   $976.15   $976.10