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 $66.34   12.209%   $74.4395   $74.44   $74.45   $74.40  
  Purchase #2 $204.73   11.320%   $227.9054   $227.91   $227.90   $227.90  
  Purchase #3 $166.26   8.860%   $180.9906   $180.99   $181.00   $181.00  
  Purchase #4 $217.48   13.317%   $246.4418   $246.44   $246.45   $246.40  
  Purchase #5 $155.74   13.748%   $177.1511   $177.15   $177.15   $177.20  
  Purchase #6 $136.89   13.731%   $155.6864   $155.69   $155.70   $155.70  
  Purchase #7 $238.85   4.217%   $248.9223   $248.92   $248.90   $248.90  
  7 purchase totals = $1,186.29       $1,311.5371   $1,311.54   $1,311.55   $1,311.50