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 $113.92   13.505%   $129.3049   $129.30   $129.30   $129.30  
  Purchase #2 $170.86   5.180%   $179.7105   $179.71   $179.70   $179.70  
  Purchase #3 $182.91   11.198%   $203.3923   $203.39   $203.40   $203.40  
  Purchase #4 $158.85   5.117%   $166.9784   $166.98   $167.00   $167.00  
  Purchase #5 $47.44   6.861%   $50.6949   $50.69   $50.70   $50.70  
  Purchase #6 $36.59   3.741%   $37.9588   $37.96   $37.95   $38.00  
  Purchase #7 $247.97   4.280%   $258.5831   $258.58   $258.60   $258.60  
  7 purchase totals = $958.54       $1,026.6229   $1,026.61   $1,026.65   $1,026.70