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 $89.38   8.113%   $96.6314   $96.63   $96.65   $96.60  
  Purchase #2 $211.56   3.735%   $219.4618   $219.46   $219.45   $219.50  
  Purchase #3 $82.46   8.590%   $89.5433   $89.54   $89.55   $89.50  
  Purchase #4 $207.29   11.435%   $230.9936   $230.99   $231.00   $231.00  
  Purchase #5 $206.87   13.460%   $234.7147   $234.71   $234.70   $234.70  
  Purchase #6 $44.57   5.610%   $47.0704   $47.07   $47.05   $47.10  
  Purchase #7 $120.92   3.310%   $124.9225   $124.92   $124.90   $124.90  
  7 purchase totals = $963.05       $1,043.3377   $1,043.32   $1,043.30   $1,043.30