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 $208.97   8.433%   $226.5924   $226.59   $226.60   $226.60  
  Purchase #2 $189.28   9.364%   $207.0042   $207.00   $207.00   $207.00  
  Purchase #3 $209.60   7.733%   $225.8084   $225.81   $225.80   $225.80  
  Purchase #4 $165.49   6.473%   $176.2022   $176.20   $176.20   $176.20  
  Purchase #5 $106.73   10.219%   $117.6367   $117.64   $117.65   $117.60  
  Purchase #6 $140.72   12.163%   $157.8358   $157.84   $157.85   $157.80  
  Purchase #7 $28.73   11.352%   $31.9914   $31.99   $32.00   $32.00  
  7 purchase totals = $1,049.52       $1,143.0711   $1,143.07   $1,143.10   $1,143.00