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 $235.52   11.179%   $261.8488   $261.85   $261.85   $261.80  
  Purchase #2 $53.80   12.151%   $60.3372   $60.34   $60.35   $60.30  
  Purchase #3 $243.26   4.350%   $253.8418   $253.84   $253.85   $253.80  
  Purchase #4 $138.87   13.209%   $157.2133   $157.21   $157.20   $157.20  
  Purchase #5 $185.97   12.313%   $208.8685   $208.87   $208.85   $208.90  
  Purchase #6 $33.39   10.342%   $36.8432   $36.84   $36.85   $36.80  
  Purchase #7 $132.57   11.529%   $147.854   $147.85   $147.85   $147.90  
  7 purchase totals = $1,023.38       $1,126.8068   $1,126.80   $1,126.80   $1,126.70