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 $8.35   5.500%   $8.8093   $8.81   $8.80   $8.80  
  Purchase #2 $220.56   11.151%   $245.1546   $245.15   $245.15   $245.20  
  Purchase #3 $27.29   7.579%   $29.3583   $29.36   $29.35   $29.40  
  Purchase #4 $220.52   8.657%   $239.6104   $239.61   $239.60   $239.60  
  Purchase #5 $136.90   5.646%   $144.6294   $144.63   $144.65   $144.60  
  Purchase #6 $161.92   4.530%   $169.255   $169.26   $169.25   $169.30  
  Purchase #7 $243.67   11.762%   $272.3305   $272.33   $272.35   $272.30  
  7 purchase totals = $1,019.21       $1,109.1475   $1,109.15   $1,109.15   $1,109.20