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 $48.26   3.871%   $50.1281   $50.13   $50.15   $50.10  
  Purchase #2 $241.93   12.164%   $271.3584   $271.36   $271.35   $271.40  
  Purchase #3 $158.60   3.457%   $164.0828   $164.08   $164.10   $164.10  
  Purchase #4 $235.90   3.792%   $244.8453   $244.85   $244.85   $244.80  
  Purchase #5 $13.96   11.547%   $15.572   $15.57   $15.55   $15.60  
  Purchase #6 $228.44   8.861%   $248.6821   $248.68   $248.70   $248.70  
  Purchase #7 $10.25   5.534%   $10.8172   $10.82   $10.80   $10.80  
  7 purchase totals = $937.34       $1,005.4859   $1,005.49   $1,005.50   $1,005.50