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 $124.97   13.268%   $141.551   $141.55   $141.55   $141.60  
  Purchase #2 $137.57   9.450%   $150.5704   $150.57   $150.55   $150.60  
  Purchase #3 $108.69   10.318%   $119.9046   $119.90   $119.90   $119.90  
  Purchase #4 $101.64   5.255%   $106.9812   $106.98   $107.00   $107.00  
  Purchase #5 $231.32   5.861%   $244.8777   $244.88   $244.90   $244.90  
  Purchase #6 $106.37   3.590%   $110.1887   $110.19   $110.20   $110.20  
  Purchase #7 $124.28   6.441%   $132.2849   $132.28   $132.30   $132.30  
  7 purchase totals = $934.84       $1,006.3585   $1,006.35   $1,006.40   $1,006.50