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 $160.58   11.588%   $179.188   $179.19   $179.20   $179.20  
  Purchase #2 $70.48   10.487%   $77.8712   $77.87   $77.85   $77.90  
  Purchase #3 $67.69   9.299%   $73.9845   $73.98   $74.00   $74.00  
  Purchase #4 $248.64   6.548%   $264.9209   $264.92   $264.90   $264.90  
  Purchase #5 $112.64   8.732%   $122.4757   $122.48   $122.50   $122.50  
  Purchase #6 $221.25   9.123%   $241.4346   $241.43   $241.45   $241.40  
  Purchase #7 $60.66   12.623%   $68.3171   $68.32   $68.30   $68.30  
  7 purchase totals = $941.94       $1,028.1920   $1,028.19   $1,028.20   $1,028.20