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 $80.32   9.578%   $88.013   $88.01   $88.00   $88.00  
  Purchase #2 $49.96   12.566%   $56.238   $56.24   $56.25   $56.20  
  Purchase #3 $245.75   6.703%   $262.2226   $262.22   $262.20   $262.20  
  Purchase #4 $209.55   11.556%   $233.7656   $233.77   $233.75   $233.80  
  Purchase #5 $184.36   9.491%   $201.8576   $201.86   $201.85   $201.90  
  Purchase #6 $139.25   13.472%   $158.0098   $158.01   $158.00   $158.00  
  Purchase #7 $48.69   10.536%   $53.82   $53.82   $53.80   $53.80  
  7 purchase totals = $957.88       $1,053.9266   $1,053.93   $1,053.85   $1,053.90