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 $218.95   13.419%   $248.3309   $248.33   $248.35   $248.30  
  Purchase #2 $31.70   5.479%   $33.4368   $33.44   $33.45   $33.40  
  Purchase #3 $235.98   4.233%   $245.969   $245.97   $245.95   $246.00  
  Purchase #4 $245.72   9.500%   $269.0634   $269.06   $269.05   $269.10  
  Purchase #5 $7.95   6.447%   $8.4625   $8.46   $8.45   $8.50  
  Purchase #6 $7.99   13.211%   $9.0456   $9.05   $9.05   $9.00  
  Purchase #7 $201.46   5.401%   $212.3409   $212.34   $212.35   $212.30  
  7 purchase totals = $949.75       $1,026.6491   $1,026.65   $1,026.65   $1,026.60