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 $64.25   6.854%   $68.6537   $68.65   $68.65   $68.70  
  Purchase #2 $225.80   4.569%   $236.1168   $236.12   $236.10   $236.10  
  Purchase #3 $62.44   6.821%   $66.699   $66.70   $66.70   $66.70  
  Purchase #4 $25.97   3.817%   $26.9613   $26.96   $26.95   $27.00  
  Purchase #5 $201.63   4.684%   $211.0743   $211.07   $211.05   $211.10  
  Purchase #6 $36.33   3.661%   $37.66   $37.66   $37.65   $37.70  
  Purchase #7 $92.40   9.241%   $100.9387   $100.94   $100.95   $100.90  
  7 purchase totals = $708.82       $748.1038   $748.10   $748.05   $748.20