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 $244.55   12.524%   $275.1774   $275.18   $275.20   $275.20  
  Purchase #2 $76.42   7.605%   $82.2317   $82.23   $82.25   $82.20  
  Purchase #3 $89.94   4.132%   $93.6563   $93.66   $93.65   $93.70  
  Purchase #4 $201.42   11.640%   $224.8653   $224.87   $224.85   $224.90  
  Purchase #5 $98.82   12.277%   $110.9521   $110.95   $110.95   $111.00  
  Purchase #6 $70.81   6.531%   $75.4346   $75.43   $75.45   $75.40  
  Purchase #7 $83.79   5.159%   $88.1127   $88.11   $88.10   $88.10  
  7 purchase totals = $865.75       $950.4301   $950.43   $950.45   $950.50