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 $148.46   6.555%   $158.1916   $158.19   $158.20   $158.20  
  Purchase #2 $211.84   7.267%   $227.2344   $227.23   $227.25   $227.20  
  Purchase #3 $188.72   9.672%   $206.973   $206.97   $206.95   $207.00  
  Purchase #4 $245.46   10.805%   $271.982   $271.98   $272.00   $272.00  
  Purchase #5 $81.46   5.146%   $85.6519   $85.65   $85.65   $85.70  
  Purchase #6 $48.69   4.322%   $50.7944   $50.79   $50.80   $50.80  
  Purchase #7 $60.35   10.773%   $66.8515   $66.85   $66.85   $66.90  
  7 purchase totals = $984.98       $1,067.6788   $1,067.66   $1,067.70   $1,067.80