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 $83.32   5.590%   $87.9776   $87.98   $88.00   $88.00  
  Purchase #2 $192.45   10.174%   $212.0299   $212.03   $212.05   $212.00  
  Purchase #3 $120.46   4.156%   $125.4663   $125.47   $125.45   $125.50  
  Purchase #4 $165.55   6.860%   $176.9067   $176.91   $176.90   $176.90  
  Purchase #5 $26.78   10.794%   $29.6706   $29.67   $29.65   $29.70  
  Purchase #6 $202.73   13.231%   $229.5532   $229.55   $229.55   $229.60  
  Purchase #7 $127.76   7.249%   $137.0213   $137.02   $137.00   $137.00  
  7 purchase totals = $919.05       $998.6256   $998.63   $998.60   $998.70