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 $39.62   13.355%   $44.9113   $44.91   $44.90   $44.90  
  Purchase #2 $214.97   12.701%   $242.2733   $242.27   $242.25   $242.30  
  Purchase #3 $140.61   6.438%   $149.6625   $149.66   $149.65   $149.70  
  Purchase #4 $71.83   7.337%   $77.1002   $77.10   $77.10   $77.10  
  Purchase #5 $161.96   13.758%   $184.2425   $184.24   $184.25   $184.20  
  Purchase #6 $196.46   9.111%   $214.3595   $214.36   $214.35   $214.40  
  Purchase #7 $114.52   7.650%   $123.2808   $123.28   $123.30   $123.30  
  7 purchase totals = $939.97       $1,035.8301   $1,035.82   $1,035.80   $1,035.90