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 $231.44   5.844%   $244.9654   $244.97   $244.95   $245.00  
  Purchase #2 $110.65   12.869%   $124.8895   $124.89   $124.90   $124.90  
  Purchase #3 $130.30   6.252%   $138.4464   $138.45   $138.45   $138.40  
  Purchase #4 $176.37   8.294%   $190.9981   $191.00   $191.00   $191.00  
  Purchase #5 $68.50   13.528%   $77.7667   $77.77   $77.75   $77.80  
  Purchase #6 $177.29   6.830%   $189.3989   $189.40   $189.40   $189.40  
  Purchase #7 $54.93   9.106%   $59.9319   $59.93   $59.95   $59.90  
  7 purchase totals = $949.48       $1,026.3969   $1,026.41   $1,026.40   $1,026.40