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 $76.66   11.208%   $85.2521   $85.25   $85.25   $85.30  
  Purchase #2 $245.39   3.863%   $254.8694   $254.87   $254.85   $254.90  
  Purchase #3 $209.47   12.539%   $235.7354   $235.74   $235.75   $235.70  
  Purchase #4 $168.75   5.641%   $178.2692   $178.27   $178.25   $178.30  
  Purchase #5 $201.56   9.119%   $219.9403   $219.94   $219.95   $219.90  
  Purchase #6 $67.88   12.481%   $76.3521   $76.35   $76.35   $76.40  
  Purchase #7 $134.25   5.364%   $141.4512   $141.45   $141.45   $141.50  
  7 purchase totals = $1,103.96       $1,191.8697   $1,191.87   $1,191.85   $1,192.00