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 $79.25   11.513%   $88.3741   $88.37   $88.35   $88.40  
  Purchase #2 $190.64   9.172%   $208.1255   $208.13   $208.15   $208.10  
  Purchase #3 $56.25   11.461%   $62.6968   $62.70   $62.70   $62.70  
  Purchase #4 $193.75   11.545%   $216.1184   $216.12   $216.10   $216.10  
  Purchase #5 $166.59   5.129%   $175.1344   $175.13   $175.15   $175.10  
  Purchase #6 $56.94   9.461%   $62.3271   $62.33   $62.35   $62.30  
  Purchase #7 $55.32   12.481%   $62.2245   $62.22   $62.20   $62.20  
  7 purchase totals = $798.74       $875.0008   $875.00   $875.00   $874.90