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 $248.78   10.206%   $274.1705   $274.17   $274.15   $274.20  
  Purchase #2 $29.58   5.298%   $31.1471   $31.15   $31.15   $31.10  
  Purchase #3 $144.67   3.653%   $149.9548   $149.95   $149.95   $150.00  
  Purchase #4 $24.94   4.647%   $26.099   $26.10   $26.10   $26.10  
  Purchase #5 $204.30   7.161%   $218.9299   $218.93   $218.95   $218.90  
  Purchase #6 $149.87   13.141%   $169.5644   $169.56   $169.55   $169.60  
  Purchase #7 $169.33   3.639%   $175.4919   $175.49   $175.50   $175.50  
  7 purchase totals = $971.47       $1,045.3576   $1,045.35   $1,045.35   $1,045.40