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 $248.27   5.553%   $262.0564   $262.06   $262.05   $262.10  
  Purchase #2 $220.83   3.698%   $228.9963   $229.00   $229.00   $229.00  
  Purchase #3 $199.57   5.144%   $209.8359   $209.84   $209.85   $209.80  
  Purchase #4 $30.95   10.431%   $34.1784   $34.18   $34.20   $34.20  
  Purchase #5 $124.95   11.289%   $139.0556   $139.06   $139.05   $139.10  
  Purchase #6 $134.33   11.650%   $149.9794   $149.98   $150.00   $150.00  
  Purchase #7 $12.46   3.748%   $12.927   $12.93   $12.95   $12.90  
  7 purchase totals = $971.36       $1,037.0290   $1,037.05   $1,037.10   $1,037.10