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 $82.91   3.721%   $85.9951   $86.00   $86.00   $86.00  
  Purchase #2 $176.65   13.589%   $200.655   $200.66   $200.65   $200.70  
  Purchase #3 $87.72   7.488%   $94.2885   $94.29   $94.30   $94.30  
  Purchase #4 $235.81   7.670%   $253.8966   $253.90   $253.90   $253.90  
  Purchase #5 $12.68   7.482%   $13.6287   $13.63   $13.65   $13.60  
  Purchase #6 $65.37   9.594%   $71.6416   $71.64   $71.65   $71.60  
  Purchase #7 $209.30   12.232%   $234.9016   $234.90   $234.90   $234.90  
  7 purchase totals = $870.44       $955.0071   $955.02   $955.05   $955.00