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 $191.96   5.758%   $203.0131   $203.01   $203.00   $203.00  
  Purchase #2 $96.29   8.602%   $104.5729   $104.57   $104.55   $104.60  
  Purchase #3 $178.50   8.117%   $192.9888   $192.99   $193.00   $193.00  
  Purchase #4 $51.93   8.474%   $56.3305   $56.33   $56.35   $56.30  
  Purchase #5 $51.70   13.347%   $58.6004   $58.60   $58.60   $58.60  
  Purchase #6 $6.82   5.335%   $7.1838   $7.18   $7.20   $7.20  
  Purchase #7 $51.52   5.322%   $54.2619   $54.26   $54.25   $54.30  
  7 purchase totals = $628.72       $676.9514   $676.94   $676.95   $677.00