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 $56.39   7.616%   $60.6847   $60.68   $60.70   $60.70  
  Purchase #2 $175.58   8.867%   $191.1487   $191.15   $191.15   $191.10  
  Purchase #3 $60.66   4.707%   $63.5153   $63.52   $63.50   $63.50  
  Purchase #4 $58.27   8.497%   $63.2212   $63.22   $63.20   $63.20  
  Purchase #5 $158.38   5.479%   $167.0576   $167.06   $167.05   $167.10  
  Purchase #6 $177.67   3.377%   $183.6699   $183.67   $183.65   $183.70  
  Purchase #7 $155.80   6.361%   $165.7104   $165.71   $165.70   $165.70  
  7 purchase totals = $842.75       $895.0078   $895.01   $894.95   $895.00