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 $198.45   3.781%   $205.9534   $205.95   $205.95   $206.00  
  Purchase #2 $50.33   6.193%   $53.4469   $53.45   $53.45   $53.40  
  Purchase #3 $223.28   8.379%   $241.9886   $241.99   $242.00   $242.00  
  Purchase #4 $162.84   8.276%   $176.3166   $176.32   $176.30   $176.30  
  Purchase #5 $124.60   3.872%   $129.4245   $129.42   $129.40   $129.40  
  Purchase #6 $212.34   10.434%   $234.4956   $234.50   $234.50   $234.50  
  Purchase #7 $184.52   3.841%   $191.6074   $191.61   $191.60   $191.60  
  7 purchase totals = $1,156.36       $1,233.2330   $1,233.24   $1,233.20   $1,233.20