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 $72.86   5.383%   $76.7821   $76.78   $76.80   $76.80  
  Purchase #2 $221.69   8.578%   $240.7066   $240.71   $240.70   $240.70  
  Purchase #3 $68.25   7.347%   $73.2643   $73.26   $73.25   $73.30  
  Purchase #4 $28.46   5.472%   $30.0173   $30.02   $30.00   $30.00  
  Purchase #5 $197.98   9.561%   $216.9089   $216.91   $216.90   $216.90  
  Purchase #6 $152.87   11.513%   $170.4699   $170.47   $170.45   $170.50  
  Purchase #7 $211.65   12.694%   $238.5169   $238.52   $238.50   $238.50  
  7 purchase totals = $953.76       $1,046.6660   $1,046.67   $1,046.60   $1,046.70