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 $177.25   9.278%   $193.6953   $193.70   $193.70   $193.70  
  Purchase #2 $135.55   3.747%   $140.6291   $140.63   $140.65   $140.60  
  Purchase #3 $177.98   5.804%   $188.31   $188.31   $188.30   $188.30  
  Purchase #4 $165.70   3.655%   $171.7563   $171.76   $171.75   $171.80  
  Purchase #5 $215.51   13.481%   $244.5629   $244.56   $244.55   $244.60  
  Purchase #6 $39.27   13.487%   $44.5663   $44.57   $44.55   $44.60  
  Purchase #7 $40.53   3.484%   $41.9421   $41.94   $41.95   $41.90  
  7 purchase totals = $951.79       $1,025.4620   $1,025.47   $1,025.45   $1,025.50