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 $167.52   7.205%   $179.5898   $179.59   $179.60   $179.60  
  Purchase #2 $222.42   8.670%   $241.7038   $241.70   $241.70   $241.70  
  Purchase #3 $54.33   7.779%   $58.5563   $58.56   $58.55   $58.60  
  Purchase #4 $168.26   5.731%   $177.903   $177.90   $177.90   $177.90  
  Purchase #5 $197.99   7.110%   $212.0671   $212.07   $212.05   $212.10  
  Purchase #6 $219.77   10.375%   $242.5711   $242.57   $242.55   $242.60  
  Purchase #7 $26.94   3.379%   $27.8503   $27.85   $27.85   $27.90  
  7 purchase totals = $1,057.23       $1,140.2414   $1,140.24   $1,140.20   $1,140.40