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 $165.89   7.189%   $177.8158   $177.82   $177.80   $177.80  
  Purchase #2 $114.46   12.784%   $129.0926   $129.09   $129.10   $129.10  
  Purchase #3 $167.36   13.406%   $189.7963   $189.80   $189.80   $189.80  
  Purchase #4 $97.41   10.494%   $107.6322   $107.63   $107.65   $107.60  
  Purchase #5 $142.49   3.283%   $147.1679   $147.17   $147.15   $147.20  
  Purchase #6 $33.86   9.565%   $37.0987   $37.10   $37.10   $37.10  
  Purchase #7 $135.57   10.227%   $149.4347   $149.43   $149.45   $149.40  
  7 purchase totals = $857.04       $938.0382   $938.04   $938.05   $938.00