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 $86.75   7.530%   $93.2823   $93.28   $93.30   $93.30  
  Purchase #2 $130.44   6.626%   $139.083   $139.08   $139.10   $139.10  
  Purchase #3 $148.94   9.568%   $163.1906   $163.19   $163.20   $163.20  
  Purchase #4 $221.88   6.529%   $236.3665   $236.37   $236.35   $236.40  
  Purchase #5 $204.81   8.752%   $222.735   $222.74   $222.75   $222.70  
  Purchase #6 $235.88   13.695%   $268.1838   $268.18   $268.20   $268.20  
  Purchase #7 $106.57   11.429%   $118.7499   $118.75   $118.75   $118.70  
  7 purchase totals = $1,135.27       $1,241.5911   $1,241.59   $1,241.65   $1,241.60