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 $91.77   3.181%   $94.6892   $94.69   $94.70   $94.70  
  Purchase #2 $72.71   11.446%   $81.0324   $81.03   $81.05   $81.00  
  Purchase #3 $200.59   3.321%   $207.2516   $207.25   $207.25   $207.30  
  Purchase #4 $135.32   5.671%   $142.994   $142.99   $143.00   $143.00  
  Purchase #5 $121.97   12.588%   $137.3236   $137.32   $137.30   $137.30  
  Purchase #6 $203.81   13.861%   $232.0601   $232.06   $232.05   $232.10  
  Purchase #7 $159.81   13.254%   $180.9912   $180.99   $181.00   $181.00  
  7 purchase totals = $985.98       $1,076.3421   $1,076.33   $1,076.35   $1,076.40