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 $59.43   6.616%   $63.3619   $63.36   $63.35   $63.40  
  Purchase #2 $244.74   6.662%   $261.0446   $261.04   $261.05   $261.00  
  Purchase #3 $47.32   5.579%   $49.96   $49.96   $49.95   $50.00  
  Purchase #4 $184.47   9.491%   $201.978   $201.98   $202.00   $202.00  
  Purchase #5 $123.93   8.381%   $134.3166   $134.32   $134.30   $134.30  
  Purchase #6 $97.97   12.154%   $109.8773   $109.88   $109.90   $109.90  
  Purchase #7 $188.77   13.374%   $214.0161   $214.02   $214.00   $214.00  
  7 purchase totals = $946.63       $1,034.5545   $1,034.56   $1,034.55   $1,034.60