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 $169.84   5.404%   $179.0182   $179.02   $179.00   $179.00  
  Purchase #2 $179.54   7.175%   $192.422   $192.42   $192.40   $192.40  
  Purchase #3 $15.92   3.649%   $16.5009   $16.50   $16.50   $16.50  
  Purchase #4 $45.94   6.388%   $48.8746   $48.87   $48.85   $48.90  
  Purchase #5 $15.82   6.293%   $16.8156   $16.82   $16.80   $16.80  
  Purchase #6 $53.30   13.813%   $60.6623   $60.66   $60.65   $60.70  
  Purchase #7 $29.60   5.528%   $31.2363   $31.24   $31.25   $31.20  
  7 purchase totals = $509.96       $545.5299   $545.53   $545.45   $545.50