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 $24.77   12.274%   $27.8103   $27.81   $27.80   $27.80  
  Purchase #2 $236.92   4.349%   $247.2237   $247.22   $247.20   $247.20  
  Purchase #3 $65.57   13.592%   $74.4823   $74.48   $74.50   $74.50  
  Purchase #4 $86.84   7.819%   $93.63   $93.63   $93.65   $93.60  
  Purchase #5 $239.48   12.186%   $268.663   $268.66   $268.65   $268.70  
  Purchase #6 $104.76   5.609%   $110.636   $110.64   $110.65   $110.60  
  Purchase #7 $238.29   3.371%   $246.3228   $246.32   $246.30   $246.30  
  7 purchase totals = $996.63       $1,068.7681   $1,068.76   $1,068.75   $1,068.70