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 $227.98   10.137%   $251.0903   $251.09   $251.10   $251.10  
  Purchase #2 $71.25   4.768%   $74.6472   $74.65   $74.65   $74.60  
  Purchase #3 $96.55   9.519%   $105.7406   $105.74   $105.75   $105.70  
  Purchase #4 $41.89   12.648%   $47.1882   $47.19   $47.20   $47.20  
  Purchase #5 $186.25   13.319%   $211.0566   $211.06   $211.05   $211.10  
  Purchase #6 $233.31   5.111%   $245.2345   $245.23   $245.25   $245.20  
  Purchase #7 $28.35   8.504%   $30.7609   $30.76   $30.75   $30.80  
  7 purchase totals = $885.58       $965.7183   $965.72   $965.75   $965.70