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 $25.67   4.131%   $26.7304   $26.73   $26.75   $26.70  
  Purchase #2 $170.77   6.564%   $181.9793   $181.98   $182.00   $182.00  
  Purchase #3 $237.52   10.773%   $263.108   $263.11   $263.10   $263.10  
  Purchase #4 $208.80   6.392%   $222.1465   $222.15   $222.15   $222.10  
  Purchase #5 $84.35   9.487%   $92.3523   $92.35   $92.35   $92.40  
  Purchase #6 $129.47   6.205%   $137.5036   $137.50   $137.50   $137.50  
  Purchase #7 $98.65   5.261%   $103.84   $103.84   $103.85   $103.80  
  7 purchase totals = $955.23       $1,027.6601   $1,027.66   $1,027.70   $1,027.60