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 $92.65   3.612%   $95.9965   $96.00   $96.00   $96.00  
  Purchase #2 $61.30   4.113%   $63.8213   $63.82   $63.80   $63.80  
  Purchase #3 $131.75   12.767%   $148.5705   $148.57   $148.55   $148.60  
  Purchase #4 $179.73   11.682%   $200.7261   $200.73   $200.75   $200.70  
  Purchase #5 $232.31   5.272%   $244.5574   $244.56   $244.55   $244.60  
  Purchase #6 $62.48   6.780%   $66.7161   $66.72   $66.70   $66.70  
  Purchase #7 $7.36   6.761%   $7.8576   $7.86   $7.85   $7.90  
  7 purchase totals = $767.58       $828.2455   $828.26   $828.20   $828.30