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 $180.92   11.627%   $201.9556   $201.96   $201.95   $202.00  
  Purchase #2 $162.48   3.116%   $167.5429   $167.54   $167.55   $167.50  
  Purchase #3 $73.88   6.849%   $78.94   $78.94   $78.95   $78.90  
  Purchase #4 $78.69   4.201%   $81.9958   $82.00   $82.00   $82.00  
  Purchase #5 $20.98   6.854%   $22.418   $22.42   $22.40   $22.40  
  Purchase #6 $200.71   7.205%   $215.1712   $215.17   $215.15   $215.20  
  Purchase #7 $116.37   8.847%   $126.6653   $126.67   $126.65   $126.70  
  7 purchase totals = $834.03       $894.6888   $894.70   $894.65   $894.70