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 $168.91   10.141%   $186.0392   $186.04   $186.05   $186.00  
  Purchase #2 $167.57   10.361%   $184.9319   $184.93   $184.95   $184.90  
  Purchase #3 $144.97   10.293%   $159.8918   $159.89   $159.90   $159.90  
  Purchase #4 $67.29   4.841%   $70.5475   $70.55   $70.55   $70.50  
  Purchase #5 $74.53   9.283%   $81.4486   $81.45   $81.45   $81.40  
  Purchase #6 $241.38   7.334%   $259.0828   $259.08   $259.10   $259.10  
  Purchase #7 $88.27   8.343%   $95.6344   $95.63   $95.65   $95.60  
  7 purchase totals = $952.92       $1,037.5762   $1,037.57   $1,037.65   $1,037.40