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 $96.38   5.300%   $101.4881   $101.49   $101.50   $101.50  
  Purchase #2 $211.96   11.652%   $236.6576   $236.66   $236.65   $236.70  
  Purchase #3 $95.44   4.163%   $99.4132   $99.41   $99.40   $99.40  
  Purchase #4 $143.74   4.163%   $149.7239   $149.72   $149.70   $149.70  
  Purchase #5 $245.81   8.270%   $266.1385   $266.14   $266.15   $266.10  
  Purchase #6 $134.43   8.840%   $146.3136   $146.31   $146.30   $146.30  
  Purchase #7 $79.86   11.698%   $89.202   $89.20   $89.20   $89.20  
  7 purchase totals = $1,007.62       $1,088.9369   $1,088.93   $1,088.90   $1,088.90