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 $110.28   12.166%   $123.6967   $123.70   $123.70   $123.70  
  Purchase #2 $163.75   10.619%   $181.1386   $181.14   $181.15   $181.10  
  Purchase #3 $26.84   4.430%   $28.029   $28.03   $28.05   $28.00  
  Purchase #4 $61.68   9.284%   $67.4064   $67.41   $67.40   $67.40  
  Purchase #5 $105.50   11.578%   $117.7148   $117.71   $117.70   $117.70  
  Purchase #6 $42.30   9.418%   $46.2838   $46.28   $46.30   $46.30  
  Purchase #7 $97.62   12.402%   $109.7268   $109.73   $109.75   $109.70  
  7 purchase totals = $607.97       $673.9961   $674.00   $674.05   $673.90