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 $209.58   6.523%   $223.2509   $223.25   $223.25   $223.30  
  Purchase #2 $82.48   12.381%   $92.6918   $92.69   $92.70   $92.70  
  Purchase #3 $198.77   11.310%   $221.2509   $221.25   $221.25   $221.30  
  Purchase #4 $88.97   12.118%   $99.7514   $99.75   $99.75   $99.80  
  Purchase #5 $237.84   9.350%   $260.078   $260.08   $260.10   $260.10  
  Purchase #6 $27.33   11.591%   $30.4978   $30.50   $30.50   $30.50  
  Purchase #7 $88.97   10.212%   $98.0556   $98.06   $98.05   $98.10  
  7 purchase totals = $933.94       $1,025.5764   $1,025.58   $1,025.60   $1,025.80