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 $66.59   10.715%   $73.7251   $73.73   $73.75   $73.70  
  Purchase #2 $106.78   11.519%   $119.08   $119.08   $119.10   $119.10  
  Purchase #3 $106.26   13.669%   $120.7847   $120.78   $120.80   $120.80  
  Purchase #4 $241.83   13.221%   $273.8023   $273.80   $273.80   $273.80  
  Purchase #5 $182.59   11.851%   $204.2287   $204.23   $204.25   $204.20  
  Purchase #6 $26.95   13.831%   $30.6775   $30.68   $30.70   $30.70  
  Purchase #7 $65.47   13.263%   $74.1533   $74.15   $74.15   $74.20  
  7 purchase totals = $796.47       $896.4516   $896.45   $896.55   $896.50