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 $55.59   12.117%   $62.3258   $62.33   $62.35   $62.30  
  Purchase #2 $78.40   11.479%   $87.3995   $87.40   $87.40   $87.40  
  Purchase #3 $106.55   6.746%   $113.7379   $113.74   $113.75   $113.70  
  Purchase #4 $236.54   6.783%   $252.5845   $252.58   $252.60   $252.60  
  Purchase #5 $147.98   6.538%   $157.6549   $157.65   $157.65   $157.70  
  Purchase #6 $160.86   12.615%   $181.1525   $181.15   $181.15   $181.20  
  Purchase #7 $149.37   3.752%   $154.9744   $154.97   $154.95   $155.00  
  7 purchase totals = $935.29       $1,009.8295   $1,009.82   $1,009.85   $1,009.90