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 $59.51   3.149%   $61.384   $61.38   $61.40   $61.40  
  Purchase #2 $117.95   8.354%   $127.8035   $127.80   $127.80   $127.80  
  Purchase #3 $200.58   9.309%   $219.252   $219.25   $219.25   $219.30  
  Purchase #4 $131.62   6.428%   $140.0805   $140.08   $140.10   $140.10  
  Purchase #5 $215.90   13.656%   $245.3833   $245.38   $245.40   $245.40  
  Purchase #6 $91.58   3.197%   $94.5078   $94.51   $94.50   $94.50  
  Purchase #7 $85.62   13.607%   $97.2703   $97.27   $97.25   $97.30  
  7 purchase totals = $902.76       $985.6814   $985.67   $985.70   $985.80