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 $120.96   10.764%   $133.9801   $133.98   $134.00   $134.00  
  Purchase #2 $109.54   5.857%   $115.9558   $115.96   $115.95   $116.00  
  Purchase #3 $150.62   7.732%   $162.2659   $162.27   $162.25   $162.30  
  Purchase #4 $143.58   13.519%   $162.9906   $162.99   $163.00   $163.00  
  Purchase #5 $79.48   3.322%   $82.1203   $82.12   $82.10   $82.10  
  Purchase #6 $234.27   11.827%   $261.9771   $261.98   $262.00   $262.00  
  Purchase #7 $202.84   11.869%   $226.9151   $226.92   $226.90   $226.90  
  7 purchase totals = $1,041.29       $1,146.2049   $1,146.22   $1,146.20   $1,146.30