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 $23.46   6.424%   $24.9671   $24.97   $24.95   $25.00  
  Purchase #2 $228.86   7.336%   $245.6492   $245.65   $245.65   $245.60  
  Purchase #3 $119.84   11.567%   $133.7019   $133.70   $133.70   $133.70  
  Purchase #4 $228.96   7.822%   $246.8693   $246.87   $246.85   $246.90  
  Purchase #5 $78.34   11.376%   $87.252   $87.25   $87.25   $87.30  
  Purchase #6 $16.86   7.194%   $18.0729   $18.07   $18.05   $18.10  
  Purchase #7 $213.46   7.526%   $229.525   $229.53   $229.55   $229.50  
  7 purchase totals = $909.78       $986.0374   $986.04   $986.00   $986.10