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 $153.41   9.290%   $167.6618   $167.66   $167.65   $167.70  
  Purchase #2 $94.33   3.232%   $97.3787   $97.38   $97.40   $97.40  
  Purchase #3 $178.83   7.825%   $192.8234   $192.82   $192.80   $192.80  
  Purchase #4 $124.67   10.194%   $137.3789   $137.38   $137.40   $137.40  
  Purchase #5 $139.27   7.644%   $149.9158   $149.92   $149.90   $149.90  
  Purchase #6 $175.27   7.642%   $188.6641   $188.66   $188.65   $188.70  
  Purchase #7 $83.48   8.438%   $90.524   $90.52   $90.50   $90.50  
  7 purchase totals = $949.26       $1,024.3467   $1,024.34   $1,024.30   $1,024.40