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 $195.37   11.687%   $218.2029   $218.20   $218.20   $218.20  
  Purchase #2 $115.55   3.295%   $119.3574   $119.36   $119.35   $119.40  
  Purchase #3 $86.87   13.294%   $98.4185   $98.42   $98.40   $98.40  
  Purchase #4 $145.76   7.609%   $156.8509   $156.85   $156.85   $156.90  
  Purchase #5 $239.66   12.461%   $269.524   $269.52   $269.50   $269.50  
  Purchase #6 $147.53   10.475%   $162.9838   $162.98   $163.00   $163.00  
  Purchase #7 $59.61   8.630%   $64.7543   $64.75   $64.75   $64.80  
  7 purchase totals = $990.35       $1,090.0918   $1,090.08   $1,090.05   $1,090.20