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 $48.36   6.858%   $51.6765   $51.68   $51.70   $51.70  
  Purchase #2 $93.35   4.510%   $97.5601   $97.56   $97.55   $97.60  
  Purchase #3 $249.64   8.810%   $271.6333   $271.63   $271.65   $271.60  
  Purchase #4 $171.64   12.163%   $192.5166   $192.52   $192.50   $192.50  
  Purchase #5 $131.36   9.825%   $144.2661   $144.27   $144.25   $144.30  
  Purchase #6 $221.26   3.860%   $229.8006   $229.80   $229.80   $229.80  
  Purchase #7 $81.51   8.714%   $88.6128   $88.61   $88.60   $88.60  
  7 purchase totals = $997.12       $1,076.0660   $1,076.07   $1,076.05   $1,076.10