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 $29.42   9.634%   $32.2543   $32.25   $32.25   $32.30  
  Purchase #2 $228.98   7.829%   $246.9068   $246.91   $246.90   $246.90  
  Purchase #3 $34.88   3.290%   $36.0276   $36.03   $36.05   $36.00  
  Purchase #4 $248.54   13.284%   $281.5561   $281.56   $281.55   $281.60  
  Purchase #5 $11.58   10.175%   $12.7583   $12.76   $12.75   $12.80  
  Purchase #6 $181.74   6.738%   $193.9856   $193.99   $194.00   $194.00  
  Purchase #7 $228.25   10.632%   $252.5175   $252.52   $252.50   $252.50  
  7 purchase totals = $963.39       $1,056.0062   $1,056.02   $1,056.00   $1,056.10