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 $197.45   3.838%   $205.0281   $205.03   $205.05   $205.00  
  Purchase #2 $246.62   8.511%   $267.6098   $267.61   $267.60   $267.60  
  Purchase #3 $56.71   6.175%   $60.2118   $60.21   $60.20   $60.20  
  Purchase #4 $173.70   9.184%   $189.6526   $189.65   $189.65   $189.70  
  Purchase #5 $34.86   9.177%   $38.0591   $38.06   $38.05   $38.10  
  Purchase #6 $70.69   4.191%   $73.6526   $73.65   $73.65   $73.70  
  Purchase #7 $112.77   3.178%   $116.3538   $116.35   $116.35   $116.40  
  7 purchase totals = $892.80       $950.5678   $950.56   $950.55   $950.70