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 $10.81   7.559%   $11.6271   $11.63   $11.65   $11.60  
  Purchase #2 $167.45   4.687%   $175.2984   $175.30   $175.30   $175.30  
  Purchase #3 $45.90   11.551%   $51.2019   $51.20   $51.20   $51.20  
  Purchase #4 $228.26   7.507%   $245.3955   $245.40   $245.40   $245.40  
  Purchase #5 $211.28   13.581%   $239.9739   $239.97   $239.95   $240.00  
  Purchase #6 $92.35   9.333%   $100.969   $100.97   $100.95   $101.00  
  Purchase #7 $157.59   11.712%   $176.0469   $176.05   $176.05   $176.00  
  7 purchase totals = $913.64       $1,000.5127   $1,000.52   $1,000.50   $1,000.50