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 $243.60   13.602%   $276.7345   $276.73   $276.75   $276.70  
  Purchase #2 $197.39   11.450%   $219.9912   $219.99   $220.00   $220.00  
  Purchase #3 $72.82   6.790%   $77.7645   $77.76   $77.75   $77.80  
  Purchase #4 $93.46   8.241%   $101.162   $101.16   $101.15   $101.20  
  Purchase #5 $105.94   12.484%   $119.1655   $119.17   $119.15   $119.20  
  Purchase #6 $189.66   7.552%   $203.9831   $203.98   $204.00   $204.00  
  Purchase #7 $62.61   5.309%   $65.934   $65.93   $65.95   $65.90  
  7 purchase totals = $965.48       $1,064.7348   $1,064.72   $1,064.75   $1,064.80