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 $67.55   3.761%   $70.0906   $70.09   $70.10   $70.10  
  Purchase #2 $210.25   10.466%   $232.2548   $232.25   $232.25   $232.30  
  Purchase #3 $126.95   4.269%   $132.3695   $132.37   $132.35   $132.40  
  Purchase #4 $199.76   3.235%   $206.2222   $206.22   $206.20   $206.20  
  Purchase #5 $243.72   13.247%   $276.0056   $276.01   $276.00   $276.00  
  Purchase #6 $184.48   6.377%   $196.2443   $196.24   $196.25   $196.20  
  Purchase #7 $215.73   7.689%   $232.3175   $232.32   $232.30   $232.30  
  7 purchase totals = $1,248.44       $1,345.5045   $1,345.50   $1,345.45   $1,345.50