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 $86.39   11.356%   $96.2004   $96.20   $96.20   $96.20  
  Purchase #2 $162.65   13.532%   $184.6598   $184.66   $184.65   $184.70  
  Purchase #3 $205.69   5.179%   $216.3427   $216.34   $216.35   $216.30  
  Purchase #4 $162.61   11.436%   $181.2061   $181.21   $181.20   $181.20  
  Purchase #5 $171.53   9.171%   $187.261   $187.26   $187.25   $187.30  
  Purchase #6 $148.85   13.317%   $168.6724   $168.67   $168.65   $168.70  
  Purchase #7 $246.49   7.697%   $265.4623   $265.46   $265.45   $265.50  
  7 purchase totals = $1,184.21       $1,299.8047   $1,299.80   $1,299.75   $1,299.90