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 $148.85   13.176%   $168.4625   $168.46   $168.45   $168.50  
  Purchase #2 $196.67   3.143%   $202.8513   $202.85   $202.85   $202.90  
  Purchase #3 $222.64   11.331%   $247.8673   $247.87   $247.85   $247.90  
  Purchase #4 $177.84   6.472%   $189.3498   $189.35   $189.35   $189.30  
  Purchase #5 $237.86   6.361%   $252.9903   $252.99   $253.00   $253.00  
  Purchase #6 $66.96   6.353%   $71.214   $71.21   $71.20   $71.20  
  Purchase #7 $155.80   4.303%   $162.5041   $162.50   $162.50   $162.50  
  7 purchase totals = $1,206.62       $1,295.2393   $1,295.23   $1,295.20   $1,295.30