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 $14.62   6.191%   $15.5251   $15.53   $15.55   $15.50  
  Purchase #2 $155.62   7.298%   $166.9771   $166.98   $167.00   $167.00  
  Purchase #3 $49.83   3.571%   $51.6094   $51.61   $51.60   $51.60  
  Purchase #4 $74.76   5.222%   $78.664   $78.66   $78.65   $78.70  
  Purchase #5 $80.58   6.618%   $85.9128   $85.91   $85.90   $85.90  
  Purchase #6 $225.76   11.444%   $251.596   $251.60   $251.60   $251.60  
  Purchase #7 $118.65   11.265%   $132.0159   $132.02   $132.00   $132.00  
  7 purchase totals = $719.82       $782.3003   $782.31   $782.30   $782.30