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 $105.32   6.257%   $111.9099   $111.91   $111.90   $111.90  
  Purchase #2 $231.38   5.715%   $244.6034   $244.60   $244.60   $244.60  
  Purchase #3 $9.68   5.516%   $10.2139   $10.21   $10.20   $10.20  
  Purchase #4 $216.66   12.647%   $244.061   $244.06   $244.05   $244.10  
  Purchase #5 $173.55   8.618%   $188.5065   $188.51   $188.50   $188.50  
  Purchase #6 $175.62   3.587%   $181.9195   $181.92   $181.90   $181.90  
  Purchase #7 $48.90   7.415%   $52.5259   $52.53   $52.55   $52.50  
  7 purchase totals = $961.11       $1,033.7401   $1,033.74   $1,033.70   $1,033.70