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 $233.29   5.593%   $246.3379   $246.34   $246.35   $246.30  
  Purchase #2 $68.83   9.236%   $75.1871   $75.19   $75.20   $75.20  
  Purchase #3 $151.92   9.137%   $165.8009   $165.80   $165.80   $165.80  
  Purchase #4 $224.67   3.308%   $232.1021   $232.10   $232.10   $232.10  
  Purchase #5 $32.60   12.567%   $36.6968   $36.70   $36.70   $36.70  
  Purchase #6 $200.64   6.786%   $214.2554   $214.26   $214.25   $214.30  
  Purchase #7 $131.90   13.681%   $149.9452   $149.95   $149.95   $149.90  
  7 purchase totals = $1,043.85       $1,120.3254   $1,120.34   $1,120.35   $1,120.30