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 $66.84   12.632%   $75.2832   $75.28   $75.30   $75.30  
  Purchase #2 $115.32   3.575%   $119.4427   $119.44   $119.45   $119.40  
  Purchase #3 $248.91   6.245%   $264.4544   $264.45   $264.45   $264.50  
  Purchase #4 $101.95   7.343%   $109.4362   $109.44   $109.45   $109.40  
  Purchase #5 $176.46   4.693%   $184.7413   $184.74   $184.75   $184.70  
  Purchase #6 $102.44   5.124%   $107.689   $107.69   $107.70   $107.70  
  Purchase #7 $179.53   13.637%   $204.0125   $204.01   $204.00   $204.00  
  7 purchase totals = $991.45       $1,065.0593   $1,065.05   $1,065.10   $1,065.00