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 $114.91   5.123%   $120.7968   $120.80   $120.80   $120.80  
  Purchase #2 $132.93   4.755%   $139.2508   $139.25   $139.25   $139.30  
  Purchase #3 $58.45   4.199%   $60.9043   $60.90   $60.90   $60.90  
  Purchase #4 $204.26   8.615%   $221.857   $221.86   $221.85   $221.90  
  Purchase #5 $114.47   6.605%   $122.0307   $122.03   $122.05   $122.00  
  Purchase #6 $82.67   9.423%   $90.46   $90.46   $90.45   $90.50  
  Purchase #7 $178.42   11.613%   $199.1399   $199.14   $199.15   $199.10  
  7 purchase totals = $886.11       $954.4395   $954.44   $954.45   $954.50