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 $243.39   7.558%   $261.7854   $261.79   $261.80   $261.80  
  Purchase #2 $82.34   11.657%   $91.9384   $91.94   $91.95   $91.90  
  Purchase #3 $48.49   8.221%   $52.4764   $52.48   $52.50   $52.50  
  Purchase #4 $179.96   11.812%   $201.2169   $201.22   $201.20   $201.20  
  Purchase #5 $56.57   10.430%   $62.4703   $62.47   $62.45   $62.50  
  Purchase #6 $170.75   8.168%   $184.6969   $184.70   $184.70   $184.70  
  Purchase #7 $30.69   10.782%   $33.999   $34.00   $34.00   $34.00  
  7 purchase totals = $812.19       $888.5833   $888.60   $888.60   $888.60