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 $183.96   5.776%   $194.5855   $194.59   $194.60   $194.60  
  Purchase #2 $70.79   3.571%   $73.3179   $73.32   $73.30   $73.30  
  Purchase #3 $41.77   3.583%   $43.2666   $43.27   $43.25   $43.30  
  Purchase #4 $148.43   7.704%   $159.865   $159.87   $159.85   $159.90  
  Purchase #5 $10.96   5.536%   $11.5667   $11.57   $11.55   $11.60  
  Purchase #6 $26.86   7.634%   $28.9105   $28.91   $28.90   $28.90  
  Purchase #7 $213.43   11.733%   $238.4717   $238.47   $238.45   $238.50  
  7 purchase totals = $696.20       $749.9839   $750.00   $749.90   $750.10