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 $64.95   6.390%   $69.1003   $69.10   $69.10   $69.10  
  Purchase #2 $132.77   3.810%   $137.8285   $137.83   $137.85   $137.80  
  Purchase #3 $169.71   13.184%   $192.0846   $192.08   $192.10   $192.10  
  Purchase #4 $49.45   3.843%   $51.3504   $51.35   $51.35   $51.40  
  Purchase #5 $160.48   8.293%   $173.7886   $173.79   $173.80   $173.80  
  Purchase #6 $245.29   9.674%   $269.0194   $269.02   $269.00   $269.00  
  Purchase #7 $85.83   4.154%   $89.3954   $89.40   $89.40   $89.40  
  7 purchase totals = $908.48       $982.5672   $982.57   $982.60   $982.60