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 $141.74   3.210%   $146.2899   $146.29   $146.30   $146.30  
  Purchase #2 $201.81   7.114%   $216.1668   $216.17   $216.15   $216.20  
  Purchase #3 $23.63   9.205%   $25.8051   $25.81   $25.80   $25.80  
  Purchase #4 $147.59   3.789%   $153.1822   $153.18   $153.20   $153.20  
  Purchase #5 $194.81   5.679%   $205.8733   $205.87   $205.85   $205.90  
  Purchase #6 $52.92   13.329%   $59.9737   $59.97   $59.95   $60.00  
  Purchase #7 $241.99   5.287%   $254.784   $254.78   $254.80   $254.80  
  7 purchase totals = $1,004.49       $1,062.0750   $1,062.07   $1,062.05   $1,062.20