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 $64.52   5.851%   $68.2951   $68.30   $68.30   $68.30  
  Purchase #2 $244.61   12.605%   $275.4431   $275.44   $275.45   $275.40  
  Purchase #3 $99.81   6.349%   $106.1469   $106.15   $106.15   $106.10  
  Purchase #4 $96.34   11.712%   $107.6233   $107.62   $107.60   $107.60  
  Purchase #5 $33.96   9.614%   $37.2249   $37.22   $37.20   $37.20  
  Purchase #6 $25.95   5.240%   $27.3098   $27.31   $27.30   $27.30  
  Purchase #7 $86.46   9.416%   $94.6011   $94.60   $94.60   $94.60  
  7 purchase totals = $651.65       $716.6442   $716.64   $716.60   $716.50