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 $201.95   11.848%   $225.877   $225.88   $225.90   $225.90  
  Purchase #2 $73.59   8.641%   $79.9489   $79.95   $79.95   $79.90  
  Purchase #3 $53.98   3.467%   $55.8515   $55.85   $55.85   $55.90  
  Purchase #4 $76.47   8.629%   $83.0686   $83.07   $83.05   $83.10  
  Purchase #5 $165.49   6.156%   $175.6776   $175.68   $175.70   $175.70  
  Purchase #6 $157.60   10.589%   $174.2883   $174.29   $174.30   $174.30  
  Purchase #7 $38.39   8.333%   $41.589   $41.59   $41.60   $41.60  
  7 purchase totals = $767.47       $836.3009   $836.31   $836.35   $836.40