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 $111.41   5.209%   $117.2133   $117.21   $117.20   $117.20  
  Purchase #2 $233.30   13.308%   $264.3476   $264.35   $264.35   $264.30  
  Purchase #3 $77.84   13.459%   $88.3165   $88.32   $88.30   $88.30  
  Purchase #4 $84.49   12.372%   $94.9431   $94.94   $94.95   $94.90  
  Purchase #5 $165.27   10.807%   $183.1307   $183.13   $183.15   $183.10  
  Purchase #6 $177.26   13.775%   $201.6776   $201.68   $201.70   $201.70  
  Purchase #7 $48.69   10.346%   $53.7275   $53.73   $53.75   $53.70  
  7 purchase totals = $898.26       $1,003.3563   $1,003.36   $1,003.40   $1,003.20