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 $243.95   10.187%   $268.8012   $268.80   $268.80   $268.80  
  Purchase #2 $215.25   7.241%   $230.8363   $230.84   $230.85   $230.80  
  Purchase #3 $46.82   10.841%   $51.8958   $51.90   $51.90   $51.90  
  Purchase #4 $18.95   8.167%   $20.4976   $20.50   $20.50   $20.50  
  Purchase #5 $166.55   12.442%   $187.2722   $187.27   $187.25   $187.30  
  Purchase #6 $23.70   4.658%   $24.8039   $24.80   $24.80   $24.80  
  Purchase #7 $60.41   13.165%   $68.363   $68.36   $68.35   $68.40  
  7 purchase totals = $775.63       $852.4700   $852.47   $852.45   $852.50