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 $76.59   10.578%   $84.6917   $84.69   $84.70   $84.70  
  Purchase #2 $206.28   12.294%   $231.6401   $231.64   $231.65   $231.60  
  Purchase #3 $216.56   7.129%   $231.9986   $232.00   $232.00   $232.00  
  Purchase #4 $173.52   10.337%   $191.4568   $191.46   $191.45   $191.50  
  Purchase #5 $206.55   9.645%   $226.4717   $226.47   $226.45   $226.50  
  Purchase #6 $103.93   8.772%   $113.0467   $113.05   $113.05   $113.00  
  Purchase #7 $164.66   11.604%   $183.7671   $183.77   $183.75   $183.80  
  7 purchase totals = $1,148.09       $1,263.0727   $1,263.08   $1,263.05   $1,263.10