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 $190.34   13.791%   $216.5898   $216.59   $216.60   $216.60  
  Purchase #2 $237.92   6.687%   $253.8297   $253.83   $253.85   $253.80  
  Purchase #3 $226.69   5.283%   $238.666   $238.67   $238.65   $238.70  
  Purchase #4 $23.57   7.850%   $25.4202   $25.42   $25.40   $25.40  
  Purchase #5 $178.80   5.836%   $189.2348   $189.23   $189.25   $189.20  
  Purchase #6 $171.38   4.798%   $179.6028   $179.60   $179.60   $179.60  
  Purchase #7 $232.71   9.224%   $254.1752   $254.18   $254.20   $254.20  
  7 purchase totals = $1,261.41       $1,357.5185   $1,357.52   $1,357.55   $1,357.50