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 $47.65   9.456%   $52.1558   $52.16   $52.15   $52.20  
  Purchase #2 $228.53   10.834%   $253.2889   $253.29   $253.30   $253.30  
  Purchase #3 $202.46   3.171%   $208.88   $208.88   $208.90   $208.90  
  Purchase #4 $169.59   8.356%   $183.7609   $183.76   $183.75   $183.80  
  Purchase #5 $195.44   5.413%   $206.0192   $206.02   $206.00   $206.00  
  Purchase #6 $179.25   3.662%   $185.8141   $185.81   $185.80   $185.80  
  Purchase #7 $139.27   4.677%   $145.7837   $145.78   $145.80   $145.80  
  7 purchase totals = $1,162.19       $1,235.7026   $1,235.70   $1,235.70   $1,235.80