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 $63.58   5.153%   $66.8563   $66.86   $66.85   $66.90  
  Purchase #2 $79.42   7.465%   $85.3487   $85.35   $85.35   $85.30  
  Purchase #3 $44.47   13.417%   $50.4365   $50.44   $50.45   $50.40  
  Purchase #4 $239.60   3.430%   $247.8183   $247.82   $247.80   $247.80  
  Purchase #5 $110.70   4.370%   $115.5376   $115.54   $115.55   $115.50  
  Purchase #6 $193.65   9.295%   $211.6498   $211.65   $211.65   $211.60  
  Purchase #7 $133.92   11.186%   $148.9003   $148.90   $148.90   $148.90  
  7 purchase totals = $865.34       $926.5475   $926.56   $926.55   $926.40