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 $89.89   5.754%   $95.0623   $95.06   $95.05   $95.10  
  Purchase #2 $138.78   13.264%   $157.1878   $157.19   $157.20   $157.20  
  Purchase #3 $233.45   6.129%   $247.7582   $247.76   $247.75   $247.80  
  Purchase #4 $101.89   6.746%   $108.7635   $108.76   $108.75   $108.80  
  Purchase #5 $135.81   11.527%   $151.4648   $151.46   $151.45   $151.50  
  Purchase #6 $180.68   12.179%   $202.685   $202.69   $202.70   $202.70  
  Purchase #7 $43.60   12.431%   $49.0199   $49.02   $49.00   $49.00  
  7 purchase totals = $924.10       $1,011.9415   $1,011.94   $1,011.90   $1,012.10