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 $41.87   4.678%   $43.8287   $43.83   $43.85   $43.80  
  Purchase #2 $34.37   6.591%   $36.6353   $36.64   $36.65   $36.60  
  Purchase #3 $36.90   13.628%   $41.9287   $41.93   $41.95   $41.90  
  Purchase #4 $50.58   5.404%   $53.3133   $53.31   $53.30   $53.30  
  Purchase #5 $101.80   13.634%   $115.6794   $115.68   $115.70   $115.70  
  Purchase #6 $229.55   9.456%   $251.2562   $251.26   $251.25   $251.30  
  Purchase #7 $211.96   9.212%   $231.4858   $231.49   $231.50   $231.50  
  7 purchase totals = $707.03       $774.1274   $774.14   $774.20   $774.10