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 $111.74   13.164%   $126.4495   $126.45   $126.45   $126.40  
  Purchase #2 $186.77   8.659%   $202.9424   $202.94   $202.95   $202.90  
  Purchase #3 $33.33   11.114%   $37.0343   $37.03   $37.05   $37.00  
  Purchase #4 $144.38   12.148%   $161.9193   $161.92   $161.90   $161.90  
  Purchase #5 $179.87   13.866%   $204.8108   $204.81   $204.80   $204.80  
  Purchase #6 $222.72   10.301%   $245.6624   $245.66   $245.65   $245.70  
  Purchase #7 $115.62   3.429%   $119.5846   $119.58   $119.60   $119.60  
  7 purchase totals = $994.43       $1,098.4033   $1,098.39   $1,098.40   $1,098.30