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 $66.80   9.653%   $73.2482   $73.25   $73.25   $73.20  
  Purchase #2 $85.79   12.193%   $96.2504   $96.25   $96.25   $96.30  
  Purchase #3 $161.39   5.301%   $169.9453   $169.95   $169.95   $169.90  
  Purchase #4 $192.72   3.742%   $199.9316   $199.93   $199.95   $199.90  
  Purchase #5 $51.82   12.419%   $58.2555   $58.26   $58.25   $58.30  
  Purchase #6 $37.33   3.730%   $38.7224   $38.72   $38.70   $38.70  
  Purchase #7 $142.87   3.499%   $147.869   $147.87   $147.85   $147.90  
  7 purchase totals = $738.72       $784.2224   $784.23   $784.20   $784.20