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 $229.36   10.288%   $252.9566   $252.96   $252.95   $253.00  
  Purchase #2 $58.40   3.317%   $60.3371   $60.34   $60.35   $60.30  
  Purchase #3 $95.42   10.699%   $105.629   $105.63   $105.65   $105.60  
  Purchase #4 $236.50   7.627%   $254.5379   $254.54   $254.55   $254.50  
  Purchase #5 $128.40   5.613%   $135.6071   $135.61   $135.60   $135.60  
  Purchase #6 $138.49   12.724%   $156.1115   $156.11   $156.10   $156.10  
  Purchase #7 $67.71   7.658%   $72.8952   $72.90   $72.90   $72.90  
  7 purchase totals = $954.28       $1,038.0744   $1,038.09   $1,038.10   $1,038.00