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 $114.58   4.555%   $119.7991   $119.80   $119.80   $119.80  
  Purchase #2 $179.41   13.538%   $203.6985   $203.70   $203.70   $203.70  
  Purchase #3 $20.41   5.254%   $21.4823   $21.48   $21.50   $21.50  
  Purchase #4 $16.75   13.310%   $18.9794   $18.98   $19.00   $19.00  
  Purchase #5 $113.67   12.123%   $127.4502   $127.45   $127.45   $127.50  
  Purchase #6 $195.96   8.207%   $212.0424   $212.04   $212.05   $212.00  
  Purchase #7 $49.75   9.278%   $54.3658   $54.37   $54.35   $54.40  
  7 purchase totals = $690.53       $757.8177   $757.82   $757.85   $757.90