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 $85.26   12.578%   $95.984   $95.98   $96.00   $96.00  
  Purchase #2 $249.46   13.457%   $283.0298   $283.03   $283.05   $283.00  
  Purchase #3 $6.64   3.582%   $6.8778   $6.88   $6.90   $6.90  
  Purchase #4 $216.39   8.526%   $234.8394   $234.84   $234.85   $234.80  
  Purchase #5 $190.41   8.380%   $206.3664   $206.37   $206.35   $206.40  
  Purchase #6 $132.98   6.738%   $141.9402   $141.94   $141.95   $141.90  
  Purchase #7 $103.65   11.170%   $115.2277   $115.23   $115.25   $115.20  
  7 purchase totals = $984.79       $1,084.2653   $1,084.27   $1,084.35   $1,084.20