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 $50.59   12.702%   $57.0159   $57.02   $57.00   $57.00  
  Purchase #2 $183.31   11.271%   $203.9709   $203.97   $203.95   $204.00  
  Purchase #3 $68.31   5.355%   $71.968   $71.97   $71.95   $72.00  
  Purchase #4 $80.82   10.687%   $89.4572   $89.46   $89.45   $89.50  
  Purchase #5 $135.31   7.362%   $145.2715   $145.27   $145.25   $145.30  
  Purchase #6 $229.41   10.254%   $252.9337   $252.93   $252.95   $252.90  
  Purchase #7 $175.96   5.348%   $185.3703   $185.37   $185.35   $185.40  
  7 purchase totals = $923.71       $1,005.9875   $1,005.99   $1,005.90   $1,006.10