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 $98.54   12.619%   $110.9748   $110.97   $110.95   $111.00  
  Purchase #2 $135.87   9.569%   $148.8714   $148.87   $148.85   $148.90  
  Purchase #3 $79.62   5.366%   $83.8924   $83.89   $83.90   $83.90  
  Purchase #4 $141.93   13.302%   $160.8095   $160.81   $160.80   $160.80  
  Purchase #5 $63.50   4.137%   $66.127   $66.13   $66.15   $66.10  
  Purchase #6 $192.88   8.561%   $209.3925   $209.39   $209.40   $209.40  
  Purchase #7 $189.96   11.210%   $211.2545   $211.25   $211.25   $211.30  
  7 purchase totals = $902.30       $991.3221   $991.31   $991.30   $991.40