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 $217.57   7.703%   $234.3294   $234.33   $234.35   $234.30  
  Purchase #2 $23.96   3.227%   $24.7332   $24.73   $24.75   $24.70  
  Purchase #3 $193.94   8.386%   $210.2038   $210.20   $210.20   $210.20  
  Purchase #4 $54.37   8.209%   $58.8332   $58.83   $58.85   $58.80  
  Purchase #5 $61.86   7.714%   $66.6319   $66.63   $66.65   $66.60  
  Purchase #6 $41.45   13.216%   $46.928   $46.93   $46.95   $46.90  
  Purchase #7 $108.63   11.574%   $121.2028   $121.20   $121.20   $121.20  
  7 purchase totals = $701.78       $762.8623   $762.85   $762.95   $762.70