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 $120.95   8.322%   $131.0155   $131.02   $131.00   $131.00  
  Purchase #2 $235.81   6.484%   $251.0999   $251.10   $251.10   $251.10  
  Purchase #3 $150.63   11.164%   $167.4463   $167.45   $167.45   $167.40  
  Purchase #4 $63.54   8.841%   $69.1576   $69.16   $69.15   $69.20  
  Purchase #5 $182.76   6.153%   $194.0052   $194.01   $194.00   $194.00  
  Purchase #6 $161.86   7.236%   $173.5722   $173.57   $173.55   $173.60  
  Purchase #7 $32.94   11.591%   $36.7581   $36.76   $36.75   $36.80  
  7 purchase totals = $948.49       $1,023.0548   $1,023.07   $1,023.00   $1,023.10