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 $240.92   13.817%   $274.2079   $274.21   $274.20   $274.20  
  Purchase #2 $127.94   9.376%   $139.9357   $139.94   $139.95   $139.90  
  Purchase #3 $198.80   13.799%   $226.2324   $226.23   $226.25   $226.20  
  Purchase #4 $228.81   11.822%   $255.8599   $255.86   $255.85   $255.90  
  Purchase #5 $166.92   13.523%   $189.4926   $189.49   $189.50   $189.50  
  Purchase #6 $44.71   9.789%   $49.0867   $49.09   $49.10   $49.10  
  Purchase #7 $64.90   9.425%   $71.0168   $71.02   $71.00   $71.00  
  7 purchase totals = $1,073.00       $1,205.8320   $1,205.84   $1,205.85   $1,205.80