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 $148.85   8.278%   $161.1718   $161.17   $161.15   $161.20  
  Purchase #2 $238.42   11.829%   $266.6227   $266.62   $266.60   $266.60  
  Purchase #3 $232.27   4.248%   $242.1368   $242.14   $242.15   $242.10  
  Purchase #4 $168.93   11.731%   $188.7472   $188.75   $188.75   $188.70  
  Purchase #5 $171.54   12.766%   $193.4388   $193.44   $193.45   $193.40  
  Purchase #6 $69.71   11.115%   $77.4583   $77.46   $77.45   $77.50  
  Purchase #7 $247.26   3.363%   $255.5754   $255.58   $255.60   $255.60  
  7 purchase totals = $1,276.98       $1,385.1510   $1,385.16   $1,385.15   $1,385.10