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 $114.53   7.833%   $123.5011   $123.50   $123.50   $123.50  
  Purchase #2 $110.42   7.820%   $119.0548   $119.05   $119.05   $119.10  
  Purchase #3 $225.52   8.566%   $244.838   $244.84   $244.85   $244.80  
  Purchase #4 $99.48   5.398%   $104.8499   $104.85   $104.85   $104.80  
  Purchase #5 $56.49   6.672%   $60.259   $60.26   $60.25   $60.30  
  Purchase #6 $250.65   7.621%   $269.752   $269.75   $269.75   $269.80  
  Purchase #7 $178.82   4.727%   $187.2728   $187.27   $187.25   $187.30  
  7 purchase totals = $1,035.91       $1,109.5276   $1,109.52   $1,109.50   $1,109.60