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 $194.52   13.182%   $220.1616   $220.16   $220.15   $220.20  
  Purchase #2 $145.97   4.548%   $152.6087   $152.61   $152.60   $152.60  
  Purchase #3 $49.50   5.569%   $52.2567   $52.26   $52.25   $52.30  
  Purchase #4 $197.94   3.747%   $205.3568   $205.36   $205.35   $205.40  
  Purchase #5 $220.96   10.669%   $244.5342   $244.53   $244.55   $244.50  
  Purchase #6 $250.60   5.514%   $264.4181   $264.42   $264.40   $264.40  
  Purchase #7 $176.42   4.843%   $184.964   $184.96   $184.95   $185.00  
  7 purchase totals = $1,235.91       $1,324.3001   $1,324.30   $1,324.25   $1,324.40