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 $52.66   11.595%   $58.7659   $58.77   $58.75   $58.80  
  Purchase #2 $186.83   5.764%   $197.5989   $197.60   $197.60   $197.60  
  Purchase #3 $145.97   6.406%   $155.3208   $155.32   $155.30   $155.30  
  Purchase #4 $49.98   7.453%   $53.705   $53.71   $53.70   $53.70  
  Purchase #5 $98.73   11.679%   $110.2607   $110.26   $110.25   $110.30  
  Purchase #6 $190.33   13.609%   $216.232   $216.23   $216.25   $216.20  
  Purchase #7 $68.61   8.606%   $74.5146   $74.51   $74.50   $74.50  
  7 purchase totals = $793.11       $866.3979   $866.40   $866.35   $866.40