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 $154.63   8.405%   $167.6267   $167.63   $167.65   $167.60  
  Purchase #2 $25.29   4.247%   $26.3641   $26.36   $26.35   $26.40  
  Purchase #3 $132.82   8.674%   $144.3408   $144.34   $144.35   $144.30  
  Purchase #4 $230.44   4.699%   $241.2684   $241.27   $241.25   $241.30  
  Purchase #5 $63.55   7.766%   $68.4853   $68.49   $68.50   $68.50  
  Purchase #6 $67.72   5.333%   $71.3315   $71.33   $71.35   $71.30  
  Purchase #7 $58.66   12.513%   $66.0001   $66.00   $66.00   $66.00  
  7 purchase totals = $733.11       $785.4169   $785.42   $785.45   $785.40