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 $70.97   3.137%   $73.1963   $73.20   $73.20   $73.20  
  Purchase #2 $174.36   9.383%   $190.7202   $190.72   $190.70   $190.70  
  Purchase #3 $223.76   4.357%   $233.5092   $233.51   $233.50   $233.50  
  Purchase #4 $152.71   7.843%   $164.687   $164.69   $164.70   $164.70  
  Purchase #5 $56.98   9.233%   $62.241   $62.24   $62.25   $62.20  
  Purchase #6 $118.27   6.624%   $126.1042   $126.10   $126.10   $126.10  
  Purchase #7 $91.51   3.535%   $94.7449   $94.74   $94.75   $94.70  
  7 purchase totals = $888.56       $945.2028   $945.20   $945.20   $945.10