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 $241.83   10.681%   $267.6599   $267.66   $267.65   $267.70  
  Purchase #2 $197.68   9.711%   $216.8767   $216.88   $216.90   $216.90  
  Purchase #3 $89.56   3.131%   $92.3641   $92.36   $92.35   $92.40  
  Purchase #4 $127.78   3.327%   $132.0312   $132.03   $132.05   $132.00  
  Purchase #5 $12.43   11.294%   $13.8338   $13.83   $13.85   $13.80  
  Purchase #6 $105.69   6.218%   $112.2618   $112.26   $112.25   $112.30  
  Purchase #7 $213.69   5.395%   $225.2186   $225.22   $225.20   $225.20  
  7 purchase totals = $988.66       $1,060.2461   $1,060.24   $1,060.25   $1,060.30