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 $49.86   6.489%   $53.0954   $53.10   $53.10   $53.10  
  Purchase #2 $231.58   4.116%   $241.1118   $241.11   $241.10   $241.10  
  Purchase #3 $160.51   8.332%   $173.8837   $173.88   $173.90   $173.90  
  Purchase #4 $69.96   7.205%   $75.0006   $75.00   $75.00   $75.00  
  Purchase #5 $214.39   10.858%   $237.6685   $237.67   $237.65   $237.70  
  Purchase #6 $6.88   5.254%   $7.2415   $7.24   $7.25   $7.20  
  Purchase #7 $10.69   5.204%   $11.2463   $11.25   $11.25   $11.20  
  7 purchase totals = $743.87       $799.2478   $799.25   $799.25   $799.20