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 $225.51   9.369%   $246.638   $246.64   $246.65   $246.60  
  Purchase #2 $57.80   8.444%   $62.6806   $62.68   $62.70   $62.70  
  Purchase #3 $173.88   8.471%   $188.6094   $188.61   $188.60   $188.60  
  Purchase #4 $67.48   3.746%   $70.0078   $70.01   $70.00   $70.00  
  Purchase #5 $215.53   3.534%   $223.1468   $223.15   $223.15   $223.10  
  Purchase #6 $11.39   10.263%   $12.559   $12.56   $12.55   $12.60  
  Purchase #7 $111.92   4.487%   $116.9419   $116.94   $116.95   $116.90  
  7 purchase totals = $863.51       $920.5835   $920.59   $920.60   $920.50