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 $121.57   8.540%   $131.9521   $131.95   $131.95   $132.00  
  Purchase #2 $188.75   11.462%   $210.3845   $210.38   $210.40   $210.40  
  Purchase #3 $240.29   10.126%   $264.6218   $264.62   $264.60   $264.60  
  Purchase #4 $61.90   8.183%   $66.9653   $66.97   $66.95   $67.00  
  Purchase #5 $65.31   3.304%   $67.4678   $67.47   $67.45   $67.50  
  Purchase #6 $76.93   4.311%   $80.2465   $80.25   $80.25   $80.20  
  Purchase #7 $210.26   10.726%   $232.8125   $232.81   $232.80   $232.80  
  7 purchase totals = $965.01       $1,054.4505   $1,054.45   $1,054.40   $1,054.50