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 $153.96   13.862%   $175.3019   $175.30   $175.30   $175.30  
  Purchase #2 $196.41   11.164%   $218.3372   $218.34   $218.35   $218.30  
  Purchase #3 $180.76   3.623%   $187.3089   $187.31   $187.30   $187.30  
  Purchase #4 $190.56   8.469%   $206.6985   $206.70   $206.70   $206.70  
  Purchase #5 $59.46   8.670%   $64.6152   $64.62   $64.60   $64.60  
  Purchase #6 $241.79   12.607%   $272.2725   $272.27   $272.25   $272.30  
  Purchase #7 $12.83   12.851%   $14.4788   $14.48   $14.50   $14.50  
  7 purchase totals = $1,035.77       $1,139.0130   $1,139.02   $1,139.00   $1,139.00