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 $206.80   9.778%   $227.0209   $227.02   $227.00   $227.00  
  Purchase #2 $237.27   8.416%   $257.2386   $257.24   $257.25   $257.20  
  Purchase #3 $200.53   11.595%   $223.7815   $223.78   $223.80   $223.80  
  Purchase #4 $131.82   7.355%   $141.5154   $141.52   $141.50   $141.50  
  Purchase #5 $98.86   7.848%   $106.6185   $106.62   $106.60   $106.60  
  Purchase #6 $181.65   8.249%   $196.6343   $196.63   $196.65   $196.60  
  Purchase #7 $43.37   11.562%   $48.3844   $48.38   $48.40   $48.40  
  7 purchase totals = $1,100.30       $1,201.1936   $1,201.19   $1,201.20   $1,201.10