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 $61.28   5.381%   $64.5775   $64.58   $64.60   $64.60  
  Purchase #2 $247.56   11.280%   $275.4848   $275.48   $275.50   $275.50  
  Purchase #3 $45.27   3.209%   $46.7227   $46.72   $46.70   $46.70  
  Purchase #4 $61.53   3.655%   $63.7789   $63.78   $63.80   $63.80  
  Purchase #5 $72.33   6.746%   $77.2094   $77.21   $77.20   $77.20  
  Purchase #6 $29.73   11.661%   $33.1968   $33.20   $33.20   $33.20  
  Purchase #7 $190.79   3.551%   $197.565   $197.57   $197.55   $197.60  
  7 purchase totals = $708.49       $758.5351   $758.54   $758.55   $758.60