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 $82.60   12.364%   $92.8127   $92.81   $92.80   $92.80  
  Purchase #2 $217.73   13.152%   $246.3658   $246.37   $246.35   $246.40  
  Purchase #3 $112.90   12.748%   $127.2925   $127.29   $127.30   $127.30  
  Purchase #4 $229.82   5.231%   $241.8419   $241.84   $241.85   $241.80  
  Purchase #5 $22.54   7.682%   $24.2715   $24.27   $24.25   $24.30  
  Purchase #6 $177.83   13.415%   $201.6859   $201.69   $201.70   $201.70  
  Purchase #7 $119.40   4.864%   $125.2076   $125.21   $125.20   $125.20  
  7 purchase totals = $962.82       $1,059.4779   $1,059.48   $1,059.45   $1,059.50