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 $76.44   11.388%   $85.145   $85.15   $85.15   $85.10  
  Purchase #2 $92.70   3.122%   $95.5941   $95.59   $95.60   $95.60  
  Purchase #3 $162.89   9.481%   $178.3336   $178.33   $178.35   $178.30  
  Purchase #4 $167.44   12.462%   $188.3064   $188.31   $188.30   $188.30  
  Purchase #5 $126.90   9.550%   $139.019   $139.02   $139.00   $139.00  
  Purchase #6 $161.91   12.247%   $181.7391   $181.74   $181.75   $181.70  
  Purchase #7 $44.70   8.777%   $48.6233   $48.62   $48.60   $48.60  
  7 purchase totals = $832.98       $916.7605   $916.76   $916.75   $916.60