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 $138.68   9.841%   $152.3275   $152.33   $152.35   $152.30  
  Purchase #2 $239.79   5.781%   $253.6523   $253.65   $253.65   $253.70  
  Purchase #3 $113.80   9.183%   $124.2503   $124.25   $124.25   $124.30  
  Purchase #4 $99.98   6.115%   $106.0938   $106.09   $106.10   $106.10  
  Purchase #5 $196.60   8.228%   $212.7762   $212.78   $212.80   $212.80  
  Purchase #6 $114.55   8.164%   $123.9019   $123.90   $123.90   $123.90  
  Purchase #7 $50.60   8.584%   $54.9435   $54.94   $54.95   $54.90  
  7 purchase totals = $954.00       $1,027.9455   $1,027.94   $1,028.00   $1,028.00