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 $236.50   4.696%   $247.606   $247.61   $247.60   $247.60  
  Purchase #2 $226.63   3.545%   $234.664   $234.66   $234.65   $234.70  
  Purchase #3 $71.71   12.663%   $80.7906   $80.79   $80.80   $80.80  
  Purchase #4 $27.51   8.707%   $29.9053   $29.91   $29.90   $29.90  
  Purchase #5 $52.96   6.108%   $56.1948   $56.19   $56.20   $56.20  
  Purchase #6 $116.53   12.356%   $130.9284   $130.93   $130.95   $130.90  
  Purchase #7 $239.50   4.556%   $250.4116   $250.41   $250.40   $250.40  
  7 purchase totals = $971.34       $1,030.5007   $1,030.50   $1,030.50   $1,030.50