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 $208.65   11.210%   $232.0397   $232.04   $232.05   $232.00  
  Purchase #2 $139.33   8.147%   $150.6812   $150.68   $150.70   $150.70  
  Purchase #3 $49.28   13.315%   $55.8416   $55.84   $55.85   $55.80  
  Purchase #4 $132.76   7.430%   $142.6241   $142.62   $142.60   $142.60  
  Purchase #5 $37.39   5.415%   $39.4147   $39.41   $39.40   $39.40  
  Purchase #6 $104.77   12.742%   $118.1198   $118.12   $118.10   $118.10  
  Purchase #7 $95.69   9.798%   $105.0657   $105.07   $105.05   $105.10  
  7 purchase totals = $767.87       $843.7868   $843.78   $843.75   $843.70