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 $232.96   11.491%   $259.7294   $259.73   $259.75   $259.70  
  Purchase #2 $158.90   11.763%   $177.5914   $177.59   $177.60   $177.60  
  Purchase #3 $165.93   4.230%   $172.9488   $172.95   $172.95   $172.90  
  Purchase #4 $243.94   8.189%   $263.9162   $263.92   $263.90   $263.90  
  Purchase #5 $145.96   4.801%   $152.9675   $152.97   $152.95   $153.00  
  Purchase #6 $60.31   13.729%   $68.59   $68.59   $68.60   $68.60  
  Purchase #7 $55.75   13.378%   $63.2082   $63.21   $63.20   $63.20  
  7 purchase totals = $1,063.75       $1,158.9515   $1,158.96   $1,158.95   $1,158.90