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 $48.87   12.654%   $55.054   $55.05   $55.05   $55.10  
  Purchase #2 $116.95   7.713%   $125.9704   $125.97   $125.95   $126.00  
  Purchase #3 $204.70   3.166%   $211.1808   $211.18   $211.20   $211.20  
  Purchase #4 $147.28   8.678%   $160.061   $160.06   $160.05   $160.10  
  Purchase #5 $149.78   9.698%   $164.3057   $164.31   $164.30   $164.30  
  Purchase #6 $177.32   5.778%   $187.5655   $187.57   $187.55   $187.60  
  Purchase #7 $249.48   4.599%   $260.9536   $260.95   $260.95   $261.00  
  7 purchase totals = $1,094.38       $1,165.0910   $1,165.09   $1,165.05   $1,165.30