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 $103.68   11.236%   $115.3295   $115.33   $115.35   $115.30  
  Purchase #2 $178.97   10.605%   $197.9498   $197.95   $197.95   $197.90  
  Purchase #3 $53.26   12.608%   $59.975   $59.98   $60.00   $60.00  
  Purchase #4 $159.34   10.593%   $176.2189   $176.22   $176.20   $176.20  
  Purchase #5 $231.87   5.632%   $244.9289   $244.93   $244.95   $244.90  
  Purchase #6 $104.28   6.236%   $110.7829   $110.78   $110.80   $110.80  
  Purchase #7 $198.93   5.462%   $209.7956   $209.80   $209.80   $209.80  
  7 purchase totals = $1,030.33       $1,114.9806   $1,114.99   $1,115.05   $1,114.90