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 $10.35   12.265%   $11.6194   $11.62   $11.60   $11.60  
  Purchase #2 $58.52   9.806%   $64.2585   $64.26   $64.25   $64.30  
  Purchase #3 $153.72   9.469%   $168.2757   $168.28   $168.30   $168.30  
  Purchase #4 $25.33   3.793%   $26.2908   $26.29   $26.30   $26.30  
  Purchase #5 $130.39   3.501%   $134.955   $134.96   $134.95   $135.00  
  Purchase #6 $248.98   6.782%   $265.8658   $265.87   $265.85   $265.90  
  Purchase #7 $236.93   11.216%   $263.5041   $263.50   $263.50   $263.50  
  7 purchase totals = $864.22       $934.7693   $934.78   $934.75   $934.90