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 $217.49   3.708%   $225.5545   $225.55   $225.55   $225.60  
  Purchase #2 $52.90   13.342%   $59.9579   $59.96   $59.95   $60.00  
  Purchase #3 $245.96   11.378%   $273.9453   $273.95   $273.95   $273.90  
  Purchase #4 $6.65   3.698%   $6.8959   $6.90   $6.90   $6.90  
  Purchase #5 $166.45   10.551%   $184.0121   $184.01   $184.00   $184.00  
  Purchase #6 $183.48   11.736%   $205.0132   $205.01   $205.00   $205.00  
  Purchase #7 $131.89   12.138%   $147.8988   $147.90   $147.90   $147.90  
  7 purchase totals = $1,004.82       $1,103.2777   $1,103.28   $1,103.25   $1,103.30