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 $68.26   12.743%   $76.9584   $76.96   $76.95   $77.00  
  Purchase #2 $218.68   10.577%   $241.8098   $241.81   $241.80   $241.80  
  Purchase #3 $117.31   12.782%   $132.3046   $132.30   $132.30   $132.30  
  Purchase #4 $59.70   13.148%   $67.5494   $67.55   $67.55   $67.50  
  Purchase #5 $41.67   3.531%   $43.1414   $43.14   $43.15   $43.10  
  Purchase #6 $220.66   12.578%   $248.4146   $248.41   $248.40   $248.40  
  Purchase #7 $197.86   5.873%   $209.4803   $209.48   $209.50   $209.50  
  7 purchase totals = $924.14       $1,019.6585   $1,019.65   $1,019.65   $1,019.60