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 $67.63   12.243%   $75.9099   $75.91   $75.90   $75.90  
  Purchase #2 $212.98   10.841%   $236.0692   $236.07   $236.05   $236.10  
  Purchase #3 $179.51   5.131%   $188.7207   $188.72   $188.70   $188.70  
  Purchase #4 $135.78   4.821%   $142.326   $142.33   $142.35   $142.30  
  Purchase #5 $227.27   8.706%   $247.0561   $247.06   $247.05   $247.10  
  Purchase #6 $176.96   13.484%   $200.8213   $200.82   $200.80   $200.80  
  Purchase #7 $152.65   11.711%   $170.5268   $170.53   $170.55   $170.50  
  7 purchase totals = $1,152.78       $1,261.4300   $1,261.44   $1,261.40   $1,261.40