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 $235.72   11.433%   $262.6699   $262.67   $262.65   $262.70  
  Purchase #2 $161.45   12.169%   $181.0969   $181.10   $181.10   $181.10  
  Purchase #3 $213.58   11.674%   $238.5133   $238.51   $238.50   $238.50  
  Purchase #4 $96.71   4.694%   $101.2496   $101.25   $101.25   $101.20  
  Purchase #5 $148.66   9.797%   $163.2242   $163.22   $163.20   $163.20  
  Purchase #6 $55.39   8.317%   $59.9968   $60.00   $60.00   $60.00  
  Purchase #7 $228.36   12.605%   $257.1448   $257.14   $257.15   $257.10  
  7 purchase totals = $1,139.87       $1,263.8955   $1,263.89   $1,263.85   $1,263.80