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 $49.43   13.349%   $56.0284   $56.03   $56.05   $56.00  
  Purchase #2 $151.72   9.564%   $166.2305   $166.23   $166.25   $166.20  
  Purchase #3 $41.60   5.461%   $43.8718   $43.87   $43.85   $43.90  
  Purchase #4 $92.44   6.119%   $98.0964   $98.10   $98.10   $98.10  
  Purchase #5 $11.53   6.476%   $12.2767   $12.28   $12.30   $12.30  
  Purchase #6 $48.60   3.205%   $50.1576   $50.16   $50.15   $50.20  
  Purchase #7 $220.41   3.576%   $228.2919   $228.29   $228.30   $228.30  
  7 purchase totals = $615.73       $654.9533   $654.96   $655.00   $655.00