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 $96.67   10.337%   $106.6628   $106.66   $106.65   $106.70  
  Purchase #2 $119.41   4.377%   $124.6366   $124.64   $124.65   $124.60  
  Purchase #3 $64.56   11.387%   $71.9114   $71.91   $71.90   $71.90  
  Purchase #4 $94.54   13.668%   $107.4617   $107.46   $107.45   $107.50  
  Purchase #5 $105.94   7.747%   $114.1472   $114.15   $114.15   $114.10  
  Purchase #6 $99.93   6.591%   $106.5164   $106.52   $106.50   $106.50  
  Purchase #7 $189.55   7.219%   $203.2336   $203.23   $203.25   $203.20  
  7 purchase totals = $770.60       $834.5697   $834.57   $834.55   $834.50