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 $213.77   12.476%   $240.4399   $240.44   $240.45   $240.40  
  Purchase #2 $70.98   6.708%   $75.7413   $75.74   $75.75   $75.70  
  Purchase #3 $160.87   4.687%   $168.41   $168.41   $168.40   $168.40  
  Purchase #4 $156.51   8.584%   $169.9448   $169.94   $169.95   $169.90  
  Purchase #5 $60.97   10.246%   $67.217   $67.22   $67.20   $67.20  
  Purchase #6 $124.50   12.171%   $139.6529   $139.65   $139.65   $139.70  
  Purchase #7 $202.61   10.486%   $223.8557   $223.86   $223.85   $223.90  
  7 purchase totals = $990.21       $1,085.2616   $1,085.26   $1,085.25   $1,085.20