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 $184.26   11.778%   $205.9621   $205.96   $205.95   $206.00  
  Purchase #2 $85.90   7.267%   $92.1424   $92.14   $92.15   $92.10  
  Purchase #3 $145.82   13.640%   $165.7098   $165.71   $165.70   $165.70  
  Purchase #4 $76.62   7.200%   $82.1366   $82.14   $82.15   $82.10  
  Purchase #5 $34.88   3.611%   $36.1395   $36.14   $36.15   $36.10  
  Purchase #6 $92.79   4.446%   $96.9154   $96.92   $96.90   $96.90  
  Purchase #7 $203.51   12.552%   $229.0546   $229.05   $229.05   $229.10  
  7 purchase totals = $823.78       $908.0604   $908.06   $908.05   $908.00