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 $231.96   12.668%   $261.3447   $261.34   $261.35   $261.30  
  Purchase #2 $214.96   8.551%   $233.3412   $233.34   $233.35   $233.30  
  Purchase #3 $226.34   12.633%   $254.9335   $254.93   $254.95   $254.90  
  Purchase #4 $10.58   8.315%   $11.4597   $11.46   $11.45   $11.50  
  Purchase #5 $202.81   11.762%   $226.6645   $226.66   $226.65   $226.70  
  Purchase #6 $14.82   8.251%   $16.0428   $16.04   $16.05   $16.00  
  Purchase #7 $141.59   3.740%   $146.8855   $146.89   $146.90   $146.90  
  7 purchase totals = $1,043.06       $1,150.6719   $1,150.66   $1,150.70   $1,150.60