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 $126.97   10.205%   $139.9273   $139.93   $139.95   $139.90  
  Purchase #2 $109.73   13.357%   $124.3866   $124.39   $124.40   $124.40  
  Purchase #3 $71.95   12.384%   $80.8603   $80.86   $80.85   $80.90  
  Purchase #4 $191.52   5.435%   $201.9291   $201.93   $201.95   $201.90  
  Purchase #5 $227.40   10.462%   $251.1906   $251.19   $251.20   $251.20  
  Purchase #6 $236.68   12.123%   $265.3727   $265.37   $265.35   $265.40  
  Purchase #7 $166.41   3.869%   $172.8484   $172.85   $172.85   $172.80  
  7 purchase totals = $1,130.66       $1,236.5150   $1,236.52   $1,236.55   $1,236.50