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 $30.55   8.229%   $33.064   $33.06   $33.05   $33.10  
  Purchase #2 $67.83   7.716%   $73.0638   $73.06   $73.05   $73.10  
  Purchase #3 $72.38   11.474%   $80.6849   $80.68   $80.70   $80.70  
  Purchase #4 $189.51   13.626%   $215.3326   $215.33   $215.35   $215.30  
  Purchase #5 $95.82   11.655%   $106.9878   $106.99   $107.00   $107.00  
  Purchase #6 $118.53   11.168%   $131.7674   $131.77   $131.75   $131.80  
  Purchase #7 $247.29   10.469%   $273.1788   $273.18   $273.20   $273.20  
  7 purchase totals = $821.91       $914.0793   $914.07   $914.10   $914.20