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 $58.39   3.416%   $60.3846   $60.38   $60.40   $60.40  
  Purchase #2 $99.36   11.667%   $110.9523   $110.95   $110.95   $111.00  
  Purchase #3 $152.76   8.141%   $165.1962   $165.20   $165.20   $165.20  
  Purchase #4 $46.38   3.846%   $48.1638   $48.16   $48.15   $48.20  
  Purchase #5 $173.96   13.592%   $197.6046   $197.60   $197.60   $197.60  
  Purchase #6 $6.72   6.317%   $7.1445   $7.14   $7.15   $7.10  
  Purchase #7 $41.26   4.266%   $43.0202   $43.02   $43.00   $43.00  
  7 purchase totals = $578.83       $632.4662   $632.45   $632.45   $632.50