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 $44.70   8.138%   $48.3377   $48.34   $48.35   $48.30  
  Purchase #2 $63.93   12.503%   $71.9232   $71.92   $71.90   $71.90  
  Purchase #3 $96.26   8.645%   $104.5817   $104.58   $104.60   $104.60  
  Purchase #4 $207.98   12.318%   $233.599   $233.60   $233.60   $233.60  
  Purchase #5 $242.87   13.496%   $275.6477   $275.65   $275.65   $275.60  
  Purchase #6 $53.48   3.326%   $55.2587   $55.26   $55.25   $55.30  
  Purchase #7 $243.52   8.710%   $264.7306   $264.73   $264.75   $264.70  
  7 purchase totals = $952.74       $1,054.0786   $1,054.08   $1,054.10   $1,054.00