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 $58.72   3.220%   $60.6108   $60.61   $60.60   $60.60  
  Purchase #2 $248.71   8.329%   $269.4251   $269.43   $269.45   $269.40  
  Purchase #3 $174.53   8.479%   $189.3284   $189.33   $189.35   $189.30  
  Purchase #4 $65.48   7.137%   $70.1533   $70.15   $70.15   $70.20  
  Purchase #5 $232.36   10.106%   $255.8423   $255.84   $255.85   $255.80  
  Purchase #6 $44.52   5.499%   $46.9682   $46.97   $46.95   $47.00  
  Purchase #7 $157.56   5.565%   $166.3282   $166.33   $166.35   $166.30  
  7 purchase totals = $981.88       $1,058.6563   $1,058.66   $1,058.70   $1,058.60