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 $246.39   5.512%   $259.971   $259.97   $259.95   $260.00  
  Purchase #2 $68.52   6.136%   $72.7244   $72.72   $72.70   $72.70  
  Purchase #3 $13.75   9.721%   $15.0866   $15.09   $15.10   $15.10  
  Purchase #4 $220.27   9.547%   $241.2992   $241.30   $241.30   $241.30  
  Purchase #5 $68.25   3.251%   $70.4688   $70.47   $70.45   $70.50  
  Purchase #6 $96.96   6.433%   $103.1974   $103.20   $103.20   $103.20  
  Purchase #7 $167.35   5.180%   $176.0187   $176.02   $176.00   $176.00  
  7 purchase totals = $881.49       $938.7661   $938.77   $938.70   $938.80