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 $203.97   11.421%   $227.2654   $227.27   $227.25   $227.30  
  Purchase #2 $52.32   9.515%   $57.2982   $57.30   $57.30   $57.30  
  Purchase #3 $108.65   13.664%   $123.4959   $123.50   $123.50   $123.50  
  Purchase #4 $187.68   7.644%   $202.0263   $202.03   $202.05   $202.00  
  Purchase #5 $190.70   6.713%   $203.5017   $203.50   $203.50   $203.50  
  Purchase #6 $56.29   11.133%   $62.5568   $62.56   $62.55   $62.60  
  Purchase #7 $53.43   13.397%   $60.588   $60.59   $60.60   $60.60  
  7 purchase totals = $853.04       $936.7323   $936.75   $936.75   $936.80