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 $53.95   12.468%   $60.6765   $60.68   $60.70   $60.70  
  Purchase #2 $104.99   10.143%   $115.6391   $115.64   $115.65   $115.60  
  Purchase #3 $139.37   6.799%   $148.8458   $148.85   $148.85   $148.80  
  Purchase #4 $122.41   9.341%   $133.8443   $133.84   $133.85   $133.80  
  Purchase #5 $221.86   4.137%   $231.0383   $231.04   $231.05   $231.00  
  Purchase #6 $189.65   11.475%   $211.4123   $211.41   $211.40   $211.40  
  Purchase #7 $39.86   10.276%   $43.956   $43.96   $43.95   $44.00  
  7 purchase totals = $872.09       $945.4123   $945.42   $945.45   $945.30