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 $24.66   8.180%   $26.6772   $26.68   $26.70   $26.70  
  Purchase #2 $146.55   13.760%   $166.7153   $166.72   $166.70   $166.70  
  Purchase #3 $231.64   13.770%   $263.5368   $263.54   $263.55   $263.50  
  Purchase #4 $52.59   10.364%   $58.0404   $58.04   $58.05   $58.00  
  Purchase #5 $212.67   13.282%   $240.9168   $240.92   $240.90   $240.90  
  Purchase #6 $168.62   6.680%   $179.8838   $179.88   $179.90   $179.90  
  Purchase #7 $121.27   6.346%   $128.9658   $128.97   $128.95   $129.00  
  7 purchase totals = $958.00       $1,064.7361   $1,064.75   $1,064.75   $1,064.70