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 $153.60   11.784%   $171.7002   $171.70   $171.70   $171.70  
  Purchase #2 $205.43   4.394%   $214.4566   $214.46   $214.45   $214.50  
  Purchase #3 $80.26   5.521%   $84.6912   $84.69   $84.70   $84.70  
  Purchase #4 $124.28   4.389%   $129.7346   $129.73   $129.75   $129.70  
  Purchase #5 $54.88   9.365%   $60.0195   $60.02   $60.00   $60.00  
  Purchase #6 $69.44   4.609%   $72.6405   $72.64   $72.65   $72.60  
  Purchase #7 $173.97   5.645%   $183.7906   $183.79   $183.80   $183.80  
  7 purchase totals = $861.86       $917.0332   $917.03   $917.05   $917.00