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 $54.93   12.612%   $61.8578   $61.86   $61.85   $61.90  
  Purchase #2 $137.82   10.852%   $152.7762   $152.78   $152.80   $152.80  
  Purchase #3 $146.29   11.552%   $163.1894   $163.19   $163.20   $163.20  
  Purchase #4 $184.48   11.240%   $205.2156   $205.22   $205.20   $205.20  
  Purchase #5 $93.56   10.169%   $103.0741   $103.07   $103.05   $103.10  
  Purchase #6 $39.60   5.250%   $41.679   $41.68   $41.70   $41.70  
  Purchase #7 $105.47   13.695%   $119.9141   $119.91   $119.90   $119.90  
  7 purchase totals = $762.15       $847.7062   $847.71   $847.70   $847.80