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 $61.31   5.721%   $64.8175   $64.82   $64.80   $64.80  
  Purchase #2 $152.62   3.287%   $157.6366   $157.64   $157.65   $157.60  
  Purchase #3 $82.66   7.365%   $88.7479   $88.75   $88.75   $88.70  
  Purchase #4 $27.97   4.405%   $29.2021   $29.20   $29.20   $29.20  
  Purchase #5 $9.41   3.403%   $9.7302   $9.73   $9.75   $9.70  
  Purchase #6 $247.75   12.313%   $278.2555   $278.26   $278.25   $278.30  
  Purchase #7 $64.55   6.646%   $68.84   $68.84   $68.85   $68.80  
  7 purchase totals = $646.27       $697.2298   $697.24   $697.25   $697.10