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 $61.86   7.633%   $66.5818   $66.58   $66.60   $66.60  
  Purchase #2 $64.34   5.466%   $67.8568   $67.86   $67.85   $67.90  
  Purchase #3 $128.82   4.653%   $134.814   $134.81   $134.80   $134.80  
  Purchase #4 $106.73   5.853%   $112.9769   $112.98   $113.00   $113.00  
  Purchase #5 $102.63   5.376%   $108.1474   $108.15   $108.15   $108.10  
  Purchase #6 $159.96   4.828%   $167.6829   $167.68   $167.70   $167.70  
  Purchase #7 $192.45   9.465%   $210.6654   $210.67   $210.65   $210.70  
  7 purchase totals = $816.79       $868.7252   $868.73   $868.75   $868.80