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 $55.98   13.573%   $63.5782   $63.58   $63.60   $63.60  
  Purchase #2 $156.41   5.614%   $165.1909   $165.19   $165.20   $165.20  
  Purchase #3 $98.81   13.633%   $112.2808   $112.28   $112.30   $112.30  
  Purchase #4 $161.61   12.369%   $181.5995   $181.60   $181.60   $181.60  
  Purchase #5 $97.33   4.682%   $101.887   $101.89   $101.90   $101.90  
  Purchase #6 $154.92   9.840%   $170.1641   $170.16   $170.15   $170.20  
  Purchase #7 $116.75   3.830%   $121.2215   $121.22   $121.20   $121.20  
  7 purchase totals = $841.81       $915.9220   $915.92   $915.95   $916.00