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 $183.97   7.508%   $197.7825   $197.78   $197.80   $197.80  
  Purchase #2 $163.37   12.243%   $183.3714   $183.37   $183.35   $183.40  
  Purchase #3 $156.25   6.519%   $166.4359   $166.44   $166.45   $166.40  
  Purchase #4 $69.36   10.843%   $76.8807   $76.88   $76.90   $76.90  
  Purchase #5 $230.72   4.249%   $240.5233   $240.52   $240.50   $240.50  
  Purchase #6 $172.99   11.160%   $192.2957   $192.30   $192.30   $192.30  
  Purchase #7 $84.27   4.271%   $87.8692   $87.87   $87.85   $87.90  
  7 purchase totals = $1,060.93       $1,145.1587   $1,145.16   $1,145.15   $1,145.20