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 $245.35   12.207%   $275.2999   $275.30   $275.30   $275.30  
  Purchase #2 $205.27   4.460%   $214.425   $214.43   $214.45   $214.40  
  Purchase #3 $232.39   10.453%   $256.6817   $256.68   $256.70   $256.70  
  Purchase #4 $192.48   7.566%   $207.043   $207.04   $207.05   $207.00  
  Purchase #5 $175.42   10.371%   $193.6128   $193.61   $193.60   $193.60  
  Purchase #6 $166.50   12.831%   $187.8636   $187.86   $187.85   $187.90  
  Purchase #7 $44.57   8.323%   $48.2796   $48.28   $48.30   $48.30  
  7 purchase totals = $1,261.98       $1,383.2056   $1,383.20   $1,383.25   $1,383.20