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 $83.97   12.631%   $94.5763   $94.58   $94.60   $94.60  
  Purchase #2 $55.56   10.694%   $61.5016   $61.50   $61.50   $61.50  
  Purchase #3 $67.66   7.850%   $72.9713   $72.97   $72.95   $73.00  
  Purchase #4 $73.46   12.189%   $82.414   $82.41   $82.40   $82.40  
  Purchase #5 $113.84   13.306%   $128.9876   $128.99   $129.00   $129.00  
  Purchase #6 $118.72   8.670%   $129.013   $129.01   $129.00   $129.00  
  Purchase #7 $171.59   5.648%   $181.2814   $181.28   $181.30   $181.30  
  7 purchase totals = $684.80       $750.7452   $750.74   $750.75   $750.80