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 $243.67   3.284%   $251.6721   $251.67   $251.65   $251.70  
  Purchase #2 $130.50   9.834%   $143.3334   $143.33   $143.35   $143.30  
  Purchase #3 $61.87   5.442%   $65.237   $65.24   $65.25   $65.20  
  Purchase #4 $47.39   6.550%   $50.494   $50.49   $50.50   $50.50  
  Purchase #5 $12.55   13.211%   $14.208   $14.21   $14.20   $14.20  
  Purchase #6 $88.99   9.198%   $97.1753   $97.18   $97.20   $97.20  
  Purchase #7 $73.78   8.204%   $79.8329   $79.83   $79.85   $79.80  
  7 purchase totals = $658.75       $701.9527   $701.95   $702.00   $701.90