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 $9.56   8.315%   $10.3549   $10.35   $10.35   $10.40  
  Purchase #2 $15.52   8.797%   $16.8853   $16.89   $16.90   $16.90  
  Purchase #3 $213.80   6.261%   $227.186   $227.19   $227.20   $227.20  
  Purchase #4 $138.35   12.123%   $155.1222   $155.12   $155.10   $155.10  
  Purchase #5 $102.26   12.260%   $114.7971   $114.80   $114.80   $114.80  
  Purchase #6 $7.87   6.686%   $8.3962   $8.40   $8.40   $8.40  
  Purchase #7 $181.53   7.754%   $195.6058   $195.61   $195.60   $195.60  
  7 purchase totals = $668.89       $728.3475   $728.36   $728.35   $728.40