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 $204.90   10.415%   $226.2403   $226.24   $226.25   $226.20  
  Purchase #2 $235.31   11.730%   $262.9119   $262.91   $262.90   $262.90  
  Purchase #3 $71.91   7.793%   $77.5139   $77.51   $77.50   $77.50  
  Purchase #4 $63.39   11.233%   $70.5106   $70.51   $70.50   $70.50  
  Purchase #5 $129.93   6.133%   $137.8986   $137.90   $137.90   $137.90  
  Purchase #6 $21.81   11.734%   $24.3692   $24.37   $24.35   $24.40  
  Purchase #7 $205.68   12.125%   $230.6187   $230.62   $230.60   $230.60  
  7 purchase totals = $932.93       $1,030.0632   $1,030.06   $1,030.00   $1,030.00