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 $177.49   12.106%   $198.9769   $198.98   $199.00   $199.00  
  Purchase #2 $147.92   11.814%   $165.3953   $165.40   $165.40   $165.40  
  Purchase #3 $156.34   13.667%   $177.707   $177.71   $177.70   $177.70  
  Purchase #4 $200.76   12.319%   $225.4916   $225.49   $225.50   $225.50  
  Purchase #5 $73.47   12.773%   $82.8543   $82.85   $82.85   $82.90  
  Purchase #6 $246.55   12.362%   $277.0285   $277.03   $277.05   $277.00  
  Purchase #7 $37.49   5.601%   $39.5898   $39.59   $39.60   $39.60  
  7 purchase totals = $1,040.02       $1,167.0434   $1,167.05   $1,167.10   $1,167.10