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 $43.32   10.288%   $47.7768   $47.78   $47.80   $47.80  
  Purchase #2 $12.34   6.350%   $13.1236   $13.12   $13.10   $13.10  
  Purchase #3 $44.88   5.521%   $47.3578   $47.36   $47.35   $47.40  
  Purchase #4 $79.91   6.134%   $84.8117   $84.81   $84.80   $84.80  
  Purchase #5 $159.57   13.257%   $180.7242   $180.72   $180.70   $180.70  
  Purchase #6 $55.99   10.874%   $62.0784   $62.08   $62.10   $62.10  
  Purchase #7 $224.37   11.484%   $250.1367   $250.14   $250.15   $250.10  
  7 purchase totals = $620.38       $686.0092   $686.01   $686.00   $686.00