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 $62.66   11.715%   $70.0006   $70.00   $70.00   $70.00  
  Purchase #2 $180.90   4.680%   $189.3661   $189.37   $189.35   $189.40  
  Purchase #3 $138.83   7.616%   $149.4033   $149.40   $149.40   $149.40  
  Purchase #4 $153.31   13.588%   $174.1418   $174.14   $174.15   $174.10  
  Purchase #5 $175.30   9.671%   $192.2533   $192.25   $192.25   $192.30  
  Purchase #6 $53.99   12.292%   $60.6265   $60.63   $60.65   $60.60  
  Purchase #7 $140.97   6.717%   $150.439   $150.44   $150.45   $150.40  
  7 purchase totals = $905.96       $986.2306   $986.23   $986.25   $986.20