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 $204.30   10.773%   $226.3092   $226.31   $226.30   $226.30  
  Purchase #2 $213.69   12.399%   $240.1854   $240.19   $240.20   $240.20  
  Purchase #3 $165.93   12.835%   $187.2271   $187.23   $187.25   $187.20  
  Purchase #4 $91.94   4.563%   $96.1352   $96.14   $96.15   $96.10  
  Purchase #5 $187.52   6.626%   $199.9451   $199.95   $199.95   $199.90  
  Purchase #6 $170.31   13.228%   $192.8386   $192.84   $192.85   $192.80  
  Purchase #7 $207.38   4.821%   $217.3778   $217.38   $217.40   $217.40  
  7 purchase totals = $1,241.07       $1,360.0184   $1,360.04   $1,360.10   $1,359.90