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 $170.83   13.580%   $194.0287   $194.03   $194.05   $194.00  
  Purchase #2 $229.89   6.484%   $244.7961   $244.80   $244.80   $244.80  
  Purchase #3 $60.64   13.387%   $68.7579   $68.76   $68.75   $68.80  
  Purchase #4 $232.39   11.627%   $259.41   $259.41   $259.40   $259.40  
  Purchase #5 $44.28   3.811%   $45.9675   $45.97   $45.95   $46.00  
  Purchase #6 $170.25   11.208%   $189.3316   $189.33   $189.35   $189.30  
  Purchase #7 $157.41   6.763%   $168.0556   $168.06   $168.05   $168.10  
  7 purchase totals = $1,065.69       $1,170.3474   $1,170.36   $1,170.35   $1,170.40