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 $186.90   9.654%   $204.9433   $204.94   $204.95   $204.90  
  Purchase #2 $92.69   5.856%   $98.1179   $98.12   $98.10   $98.10  
  Purchase #3 $100.44   5.112%   $105.5745   $105.57   $105.55   $105.60  
  Purchase #4 $194.74   7.397%   $209.1449   $209.14   $209.15   $209.10  
  Purchase #5 $58.59   7.784%   $63.1506   $63.15   $63.15   $63.20  
  Purchase #6 $187.51   7.687%   $201.9239   $201.92   $201.90   $201.90  
  Purchase #7 $247.49   8.613%   $268.8063   $268.81   $268.80   $268.80  
  7 purchase totals = $1,068.36       $1,151.6614   $1,151.65   $1,151.60   $1,151.60