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 $61.58   12.297%   $69.1525   $69.15   $69.15   $69.20  
  Purchase #2 $228.81   9.552%   $250.6659   $250.67   $250.65   $250.70  
  Purchase #3 $230.84   13.661%   $262.3751   $262.38   $262.40   $262.40  
  Purchase #4 $52.44   5.787%   $55.4747   $55.47   $55.45   $55.50  
  Purchase #5 $87.47   12.561%   $98.4571   $98.46   $98.45   $98.50  
  Purchase #6 $75.45   12.433%   $84.8307   $84.83   $84.85   $84.80  
  Purchase #7 $122.40   3.423%   $126.5898   $126.59   $126.60   $126.60  
  7 purchase totals = $858.99       $947.5458   $947.55   $947.55   $947.70