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 $57.66   4.671%   $60.3533   $60.35   $60.35   $60.40  
  Purchase #2 $180.26   12.453%   $202.7078   $202.71   $202.70   $202.70  
  Purchase #3 $54.76   6.459%   $58.2969   $58.30   $58.30   $58.30  
  Purchase #4 $181.36   6.267%   $192.7258   $192.73   $192.75   $192.70  
  Purchase #5 $102.58   11.365%   $114.2382   $114.24   $114.25   $114.20  
  Purchase #6 $49.71   5.267%   $52.3282   $52.33   $52.35   $52.30  
  Purchase #7 $183.91   9.437%   $201.2656   $201.27   $201.25   $201.30  
  7 purchase totals = $810.24       $881.9158   $881.93   $881.95   $881.90