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 $195.61   8.795%   $212.8139   $212.81   $212.80   $212.80  
  Purchase #2 $11.36   4.787%   $11.9038   $11.90   $11.90   $11.90  
  Purchase #3 $25.99   7.788%   $28.0141   $28.01   $28.00   $28.00  
  Purchase #4 $38.50   8.426%   $41.744   $41.74   $41.75   $41.70  
  Purchase #5 $220.69   6.779%   $235.6506   $235.65   $235.65   $235.70  
  Purchase #6 $193.76   7.866%   $209.0012   $209.00   $209.00   $209.00  
  Purchase #7 $174.98   7.754%   $188.5479   $188.55   $188.55   $188.50  
  7 purchase totals = $860.89       $927.6755   $927.66   $927.65   $927.60