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 $244.81   6.121%   $259.7948   $259.79   $259.80   $259.80  
  Purchase #2 $122.46   9.816%   $134.4807   $134.48   $134.50   $134.50  
  Purchase #3 $72.65   9.819%   $79.7835   $79.78   $79.80   $79.80  
  Purchase #4 $17.32   6.673%   $18.4758   $18.48   $18.50   $18.50  
  Purchase #5 $56.62   11.733%   $63.2632   $63.26   $63.25   $63.30  
  Purchase #6 $101.59   4.363%   $106.0224   $106.02   $106.00   $106.00  
  Purchase #7 $82.77   13.784%   $94.179   $94.18   $94.20   $94.20  
  7 purchase totals = $698.22       $755.9994   $755.99   $756.05   $756.10