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 $240.53   4.390%   $251.0893   $251.09   $251.10   $251.10  
  Purchase #2 $51.74   11.316%   $57.5949   $57.59   $57.60   $57.60  
  Purchase #3 $46.77   6.810%   $49.955   $49.96   $49.95   $50.00  
  Purchase #4 $217.42   7.318%   $233.3308   $233.33   $233.35   $233.30  
  Purchase #5 $211.62   11.268%   $235.4653   $235.47   $235.45   $235.50  
  Purchase #6 $189.95   5.816%   $200.9975   $201.00   $201.00   $201.00  
  Purchase #7 $210.45   9.868%   $231.2172   $231.22   $231.20   $231.20  
  7 purchase totals = $1,168.48       $1,259.6500   $1,259.66   $1,259.65   $1,259.70