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 $110.33   7.222%   $118.298   $118.30   $118.30   $118.30  
  Purchase #2 $63.95   12.185%   $71.7423   $71.74   $71.75   $71.70  
  Purchase #3 $116.49   5.834%   $123.286   $123.29   $123.30   $123.30  
  Purchase #4 $211.99   9.731%   $232.6187   $232.62   $232.60   $232.60  
  Purchase #5 $223.69   4.299%   $233.3064   $233.31   $233.30   $233.30  
  Purchase #6 $15.85   9.405%   $17.3407   $17.34   $17.35   $17.30  
  Purchase #7 $131.36   9.429%   $143.7459   $143.75   $143.75   $143.70  
  7 purchase totals = $873.66       $940.3380   $940.35   $940.35   $940.20