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 $55.51   13.281%   $62.8823   $62.88   $62.90   $62.90  
  Purchase #2 $181.33   11.373%   $201.9527   $201.95   $201.95   $202.00  
  Purchase #3 $162.61   6.384%   $172.991   $172.99   $173.00   $173.00  
  Purchase #4 $160.93   7.303%   $172.6827   $172.68   $172.70   $172.70  
  Purchase #5 $18.76   11.794%   $20.9726   $20.97   $20.95   $21.00  
  Purchase #6 $141.44   4.102%   $147.2419   $147.24   $147.25   $147.20  
  Purchase #7 $171.86   6.481%   $182.9982   $183.00   $183.00   $183.00  
  7 purchase totals = $892.44       $961.7214   $961.71   $961.75   $961.80