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 $222.89   12.273%   $250.2453   $250.25   $250.25   $250.20  
  Purchase #2 $239.82   8.152%   $259.3701   $259.37   $259.35   $259.40  
  Purchase #3 $46.40   8.519%   $50.3528   $50.35   $50.35   $50.40  
  Purchase #4 $97.96   5.831%   $103.672   $103.67   $103.65   $103.70  
  Purchase #5 $122.55   5.418%   $129.1898   $129.19   $129.20   $129.20  
  Purchase #6 $147.51   9.807%   $161.9763   $161.98   $162.00   $162.00  
  Purchase #7 $51.43   9.712%   $56.4249   $56.42   $56.40   $56.40  
  7 purchase totals = $928.56       $1,011.2312   $1,011.23   $1,011.20   $1,011.30