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 $105.99   6.708%   $113.0998   $113.10   $113.10   $113.10  
  Purchase #2 $157.57   11.781%   $176.1333   $176.13   $176.15   $176.10  
  Purchase #3 $70.72   13.366%   $80.1724   $80.17   $80.15   $80.20  
  Purchase #4 $239.41   12.217%   $268.6587   $268.66   $268.65   $268.70  
  Purchase #5 $182.78   12.428%   $205.4959   $205.50   $205.50   $205.50  
  Purchase #6 $55.73   8.449%   $60.4386   $60.44   $60.45   $60.40  
  Purchase #7 $112.60   7.364%   $120.8919   $120.89   $120.90   $120.90  
  7 purchase totals = $924.80       $1,024.8906   $1,024.89   $1,024.90   $1,024.90