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 $23.68   6.770%   $25.2831   $25.28   $25.30   $25.30  
  Purchase #2 $15.52   7.511%   $16.6857   $16.69   $16.70   $16.70  
  Purchase #3 $5.50   3.872%   $5.713   $5.71   $5.70   $5.70  
  Purchase #4 $245.63   5.768%   $259.7979   $259.80   $259.80   $259.80  
  Purchase #5 $138.68   5.310%   $146.0439   $146.04   $146.05   $146.00  
  Purchase #6 $201.36   8.663%   $218.8038   $218.80   $218.80   $218.80  
  Purchase #7 $100.77   9.111%   $109.9512   $109.95   $109.95   $110.00  
  7 purchase totals = $731.14       $782.2786   $782.27   $782.30   $782.30