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 $211.26   4.458%   $220.678   $220.68   $220.70   $220.70  
  Purchase #2 $218.78   13.496%   $248.3065   $248.31   $248.30   $248.30  
  Purchase #3 $52.87   6.662%   $56.3922   $56.39   $56.40   $56.40  
  Purchase #4 $132.30   9.617%   $145.0233   $145.02   $145.00   $145.00  
  Purchase #5 $71.95   7.721%   $77.5053   $77.51   $77.50   $77.50  
  Purchase #6 $50.40   8.838%   $54.8544   $54.85   $54.85   $54.90  
  Purchase #7 $196.74   13.398%   $223.0992   $223.10   $223.10   $223.10  
  7 purchase totals = $934.30       $1,025.8589   $1,025.86   $1,025.85   $1,025.90