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 $35.52   6.134%   $37.6988   $37.70   $37.70   $37.70  
  Purchase #2 $208.73   4.728%   $218.5988   $218.60   $218.60   $218.60  
  Purchase #3 $249.72   10.713%   $276.4725   $276.47   $276.45   $276.50  
  Purchase #4 $56.78   6.789%   $60.6348   $60.63   $60.65   $60.60  
  Purchase #5 $120.96   4.316%   $126.1806   $126.18   $126.20   $126.20  
  Purchase #6 $152.46   9.513%   $166.9635   $166.96   $166.95   $167.00  
  Purchase #7 $54.81   13.645%   $62.2888   $62.29   $62.30   $62.30  
  7 purchase totals = $878.98       $948.8378   $948.83   $948.85   $948.90