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 $56.96   12.268%   $63.9479   $63.95   $63.95   $63.90  
  Purchase #2 $134.52   8.844%   $146.4169   $146.42   $146.40   $146.40  
  Purchase #3 $23.90   6.141%   $25.3677   $25.37   $25.35   $25.40  
  Purchase #4 $161.92   11.824%   $181.0654   $181.07   $181.05   $181.10  
  Purchase #5 $28.27   3.573%   $29.2801   $29.28   $29.30   $29.30  
  Purchase #6 $21.67   4.122%   $22.5632   $22.56   $22.55   $22.60  
  Purchase #7 $96.42   4.407%   $100.6692   $100.67   $100.65   $100.70  
  7 purchase totals = $523.66       $569.3104   $569.32   $569.25   $569.40