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 $88.38   11.108%   $98.1973   $98.20   $98.20   $98.20  
  Purchase #2 $85.68   11.165%   $95.2462   $95.25   $95.25   $95.20  
  Purchase #3 $218.66   8.778%   $237.854   $237.85   $237.85   $237.90  
  Purchase #4 $31.41   9.519%   $34.3999   $34.40   $34.40   $34.40  
  Purchase #5 $154.81   12.576%   $174.2789   $174.28   $174.30   $174.30  
  Purchase #6 $50.76   3.562%   $52.5681   $52.57   $52.55   $52.60  
  Purchase #7 $79.43   5.488%   $83.7891   $83.79   $83.80   $83.80  
  7 purchase totals = $709.13       $776.3335   $776.34   $776.35   $776.40