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 $52.64   7.462%   $56.568   $56.57   $56.55   $56.60  
  Purchase #2 $142.74   4.112%   $148.6095   $148.61   $148.60   $148.60  
  Purchase #3 $73.58   4.351%   $76.7815   $76.78   $76.80   $76.80  
  Purchase #4 $201.43   6.467%   $214.4565   $214.46   $214.45   $214.50  
  Purchase #5 $195.49   4.288%   $203.8726   $203.87   $203.85   $203.90  
  Purchase #6 $194.94   4.510%   $203.7318   $203.73   $203.75   $203.70  
  Purchase #7 $167.58   6.125%   $177.8443   $177.84   $177.85   $177.80  
  7 purchase totals = $1,028.40       $1,081.8642   $1,081.86   $1,081.85   $1,081.90