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 $57.92   6.341%   $61.5927   $61.59   $61.60   $61.60  
  Purchase #2 $86.29   10.600%   $95.4367   $95.44   $95.45   $95.40  
  Purchase #3 $11.87   13.654%   $13.4907   $13.49   $13.50   $13.50  
  Purchase #4 $121.75   6.650%   $129.8464   $129.85   $129.85   $129.80  
  Purchase #5 $246.70   9.800%   $270.8766   $270.88   $270.90   $270.90  
  Purchase #6 $122.66   9.785%   $134.6623   $134.66   $134.65   $134.70  
  Purchase #7 $89.49   6.352%   $95.1744   $95.17   $95.15   $95.20  
  7 purchase totals = $736.68       $801.0798   $801.08   $801.10   $801.10