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 $190.58   7.757%   $205.3633   $205.36   $205.35   $205.40  
  Purchase #2 $118.74   13.663%   $134.9634   $134.96   $134.95   $135.00  
  Purchase #3 $45.57   3.636%   $47.2269   $47.23   $47.25   $47.20  
  Purchase #4 $125.59   5.572%   $132.5879   $132.59   $132.60   $132.60  
  Purchase #5 $56.30   13.373%   $63.829   $63.83   $63.85   $63.80  
  Purchase #6 $136.53   8.316%   $147.8838   $147.88   $147.90   $147.90  
  Purchase #7 $106.32   3.526%   $110.0688   $110.07   $110.05   $110.10  
  7 purchase totals = $779.63       $841.9231   $841.92   $841.95   $842.00