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 $171.54   5.275%   $180.5887   $180.59   $180.60   $180.60  
  Purchase #2 $20.28   11.492%   $22.6106   $22.61   $22.60   $22.60  
  Purchase #3 $86.75   10.648%   $95.9871   $95.99   $96.00   $96.00  
  Purchase #4 $248.26   10.504%   $274.3372   $274.34   $274.35   $274.30  
  Purchase #5 $108.82   9.814%   $119.4996   $119.50   $119.50   $119.50  
  Purchase #6 $190.34   8.487%   $206.4942   $206.49   $206.50   $206.50  
  Purchase #7 $134.85   11.425%   $150.2566   $150.26   $150.25   $150.30  
  7 purchase totals = $960.84       $1,049.7740   $1,049.78   $1,049.80   $1,049.80