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 $226.69   6.781%   $242.0618   $242.06   $242.05   $242.10  
  Purchase #2 $41.84   9.442%   $45.7905   $45.79   $45.80   $45.80  
  Purchase #3 $114.99   6.475%   $122.4356   $122.44   $122.45   $122.40  
  Purchase #4 $113.96   3.516%   $117.9668   $117.97   $117.95   $118.00  
  Purchase #5 $150.70   9.134%   $164.4649   $164.46   $164.45   $164.50  
  Purchase #6 $106.53   5.654%   $112.5532   $112.55   $112.55   $112.60  
  Purchase #7 $127.80   6.345%   $135.9089   $135.91   $135.90   $135.90  
  7 purchase totals = $882.51       $941.1817   $941.18   $941.15   $941.30