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 $29.81   10.506%   $32.9418   $32.94   $32.95   $32.90  
  Purchase #2 $212.82   11.588%   $237.4816   $237.48   $237.50   $237.50  
  Purchase #3 $58.44   9.393%   $63.9293   $63.93   $63.95   $63.90  
  Purchase #4 $183.53   12.322%   $206.1446   $206.14   $206.15   $206.10  
  Purchase #5 $99.27   10.671%   $109.8631   $109.86   $109.85   $109.90  
  Purchase #6 $203.98   5.866%   $215.9455   $215.95   $215.95   $215.90  
  Purchase #7 $237.70   3.570%   $246.1859   $246.19   $246.20   $246.20  
  7 purchase totals = $1,025.55       $1,112.4918   $1,112.49   $1,112.55   $1,112.40