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 $109.74   6.668%   $117.0575   $117.06   $117.05   $117.10  
  Purchase #2 $236.46   11.442%   $263.5158   $263.52   $263.50   $263.50  
  Purchase #3 $61.49   3.516%   $63.652   $63.65   $63.65   $63.70  
  Purchase #4 $88.29   3.328%   $91.2283   $91.23   $91.25   $91.20  
  Purchase #5 $97.43   5.290%   $102.584   $102.58   $102.60   $102.60  
  Purchase #6 $220.44   11.823%   $246.5026   $246.50   $246.50   $246.50  
  Purchase #7 $195.60   5.771%   $206.8881   $206.89   $206.90   $206.90  
  7 purchase totals = $1,009.45       $1,091.4283   $1,091.43   $1,091.45   $1,091.50