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 $60.32   11.330%   $67.1543   $67.15   $67.15   $67.20  
  Purchase #2 $222.51   10.640%   $246.1851   $246.19   $246.20   $246.20  
  Purchase #3 $72.68   3.384%   $75.1395   $75.14   $75.15   $75.10  
  Purchase #4 $226.69   5.194%   $238.4643   $238.46   $238.45   $238.50  
  Purchase #5 $24.62   11.280%   $27.3971   $27.40   $27.40   $27.40  
  Purchase #6 $5.70   5.699%   $6.0248   $6.02   $6.00   $6.00  
  Purchase #7 $218.93   10.213%   $241.2893   $241.29   $241.30   $241.30  
  7 purchase totals = $831.45       $901.6544   $901.65   $901.65   $901.70