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 $70.41   8.861%   $76.649   $76.65   $76.65   $76.60  
  Purchase #2 $148.28   5.567%   $156.5347   $156.53   $156.55   $156.50  
  Purchase #3 $199.89   5.151%   $210.1863   $210.19   $210.20   $210.20  
  Purchase #4 $236.71   4.653%   $247.7241   $247.72   $247.70   $247.70  
  Purchase #5 $32.84   5.447%   $34.6288   $34.63   $34.65   $34.60  
  Purchase #6 $234.77   7.210%   $251.6969   $251.70   $251.70   $251.70  
  Purchase #7 $18.39   12.380%   $20.6667   $20.67   $20.65   $20.70  
  7 purchase totals = $941.29       $998.0865   $998.09   $998.10   $998.00