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 $226.43   12.653%   $255.0802   $255.08   $255.10   $255.10  
  Purchase #2 $54.69   8.786%   $59.4951   $59.50   $59.50   $59.50  
  Purchase #3 $104.59   3.428%   $108.1753   $108.18   $108.20   $108.20  
  Purchase #4 $161.70   8.812%   $175.949   $175.95   $175.95   $175.90  
  Purchase #5 $236.91   4.381%   $247.289   $247.29   $247.30   $247.30  
  Purchase #6 $232.91   5.705%   $246.1975   $246.20   $246.20   $246.20  
  Purchase #7 $213.72   9.360%   $233.7242   $233.72   $233.70   $233.70  
  7 purchase totals = $1,230.95       $1,325.9103   $1,325.92   $1,325.95   $1,325.90