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 $239.93   5.546%   $253.2365   $253.24   $253.25   $253.20  
  Purchase #2 $94.34   7.633%   $101.541   $101.54   $101.55   $101.50  
  Purchase #3 $110.25   7.170%   $118.1549   $118.15   $118.15   $118.20  
  Purchase #4 $24.68   5.189%   $25.9606   $25.96   $25.95   $26.00  
  Purchase #5 $146.97   5.692%   $155.3355   $155.34   $155.35   $155.30  
  Purchase #6 $108.76   9.621%   $119.2238   $119.22   $119.20   $119.20  
  Purchase #7 $175.86   12.321%   $197.5277   $197.53   $197.55   $197.50  
  7 purchase totals = $900.79       $970.9800   $970.98   $971.00   $970.90