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 $64.73   7.567%   $69.6281   $69.63   $69.65   $69.60  
  Purchase #2 $219.82   10.699%   $243.3385   $243.34   $243.35   $243.30  
  Purchase #3 $148.76   7.854%   $160.4436   $160.44   $160.45   $160.40  
  Purchase #4 $68.94   9.769%   $75.6747   $75.67   $75.65   $75.70  
  Purchase #5 $52.84   7.586%   $56.8484   $56.85   $56.85   $56.80  
  Purchase #6 $61.93   3.371%   $64.0177   $64.02   $64.00   $64.00  
  Purchase #7 $164.93   5.239%   $173.5707   $173.57   $173.55   $173.60  
  7 purchase totals = $781.95       $843.5217   $843.52   $843.50   $843.40