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 $41.98   5.594%   $44.3284   $44.33   $44.35   $44.30  
  Purchase #2 $208.89   12.804%   $235.6363   $235.64   $235.65   $235.60  
  Purchase #3 $157.55   6.710%   $168.1216   $168.12   $168.10   $168.10  
  Purchase #4 $60.89   5.411%   $64.1848   $64.18   $64.20   $64.20  
  Purchase #5 $36.40   11.189%   $40.4728   $40.47   $40.45   $40.50  
  Purchase #6 $181.76   11.489%   $202.6424   $202.64   $202.65   $202.60  
  Purchase #7 $153.82   6.405%   $163.6722   $163.67   $163.65   $163.70  
  7 purchase totals = $841.29       $919.0585   $919.05   $919.05   $919.00