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 $246.30   8.718%   $267.7724   $267.77   $267.75   $267.80  
  Purchase #2 $167.69   4.327%   $174.9459   $174.95   $174.95   $174.90  
  Purchase #3 $23.52   7.317%   $25.241   $25.24   $25.25   $25.20  
  Purchase #4 $145.76   13.196%   $164.9945   $164.99   $165.00   $165.00  
  Purchase #5 $234.31   9.693%   $257.0217   $257.02   $257.00   $257.00  
  Purchase #6 $70.51   6.567%   $75.1404   $75.14   $75.15   $75.10  
  Purchase #7 $81.82   3.139%   $84.3883   $84.39   $84.40   $84.40  
  7 purchase totals = $969.91       $1,049.5042   $1,049.50   $1,049.50   $1,049.40