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 $145.58   5.526%   $153.6248   $153.62   $153.60   $153.60  
  Purchase #2 $164.57   9.351%   $179.9589   $179.96   $179.95   $180.00  
  Purchase #3 $165.87   11.247%   $184.5254   $184.53   $184.55   $184.50  
  Purchase #4 $146.84   6.184%   $155.9206   $155.92   $155.90   $155.90  
  Purchase #5 $45.64   8.779%   $49.6467   $49.65   $49.65   $49.60  
  Purchase #6 $73.71   3.336%   $76.169   $76.17   $76.15   $76.20  
  Purchase #7 $57.55   9.539%   $63.0397   $63.04   $63.05   $63.00  
  7 purchase totals = $799.76       $862.8851   $862.89   $862.85   $862.80