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 $63.33   8.846%   $68.9322   $68.93   $68.95   $68.90  
  Purchase #2 $191.62   5.755%   $202.6477   $202.65   $202.65   $202.60  
  Purchase #3 $28.48   6.847%   $30.43   $30.43   $30.45   $30.40  
  Purchase #4 $23.46   10.233%   $25.8607   $25.86   $25.85   $25.90  
  Purchase #5 $241.56   5.800%   $255.5705   $255.57   $255.55   $255.60  
  Purchase #6 $182.29   6.252%   $193.6868   $193.69   $193.70   $193.70  
  Purchase #7 $71.74   4.151%   $74.7179   $74.72   $74.70   $74.70  
  7 purchase totals = $802.48       $851.8458   $851.85   $851.85   $851.80