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 $250.75   10.190%   $276.3014   $276.30   $276.30   $276.30  
  Purchase #2 $192.78   8.330%   $208.8386   $208.84   $208.85   $208.80  
  Purchase #3 $22.92   11.618%   $25.5828   $25.58   $25.60   $25.60  
  Purchase #4 $71.89   12.684%   $81.0085   $81.01   $81.00   $81.00  
  Purchase #5 $87.75   10.159%   $96.6645   $96.66   $96.65   $96.70  
  Purchase #6 $120.97   12.522%   $136.1179   $136.12   $136.10   $136.10  
  Purchase #7 $127.35   3.702%   $132.0645   $132.06   $132.05   $132.10  
  7 purchase totals = $874.41       $956.5782   $956.57   $956.55   $956.60