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 $44.92   12.611%   $50.5849   $50.58   $50.60   $50.60  
  Purchase #2 $161.85   13.444%   $183.6091   $183.61   $183.60   $183.60  
  Purchase #3 $105.37   12.639%   $118.6877   $118.69   $118.70   $118.70  
  Purchase #4 $90.46   9.382%   $98.947   $98.95   $98.95   $98.90  
  Purchase #5 $187.94   12.297%   $211.051   $211.05   $211.05   $211.10  
  Purchase #6 $79.52   6.132%   $84.3962   $84.40   $84.40   $84.40  
  Purchase #7 $50.65   11.424%   $56.4363   $56.44   $56.45   $56.40  
  7 purchase totals = $720.71       $803.7122   $803.72   $803.75   $803.70