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 $66.87   3.818%   $69.4231   $69.42   $69.40   $69.40  
  Purchase #2 $152.68   5.819%   $161.5644   $161.56   $161.55   $161.60  
  Purchase #3 $113.99   4.469%   $119.0842   $119.08   $119.10   $119.10  
  Purchase #4 $228.84   4.387%   $238.8792   $238.88   $238.90   $238.90  
  Purchase #5 $180.65   9.162%   $197.2012   $197.20   $197.20   $197.20  
  Purchase #6 $8.40   4.417%   $8.771   $8.77   $8.75   $8.80  
  Purchase #7 $73.65   3.390%   $76.1467   $76.15   $76.15   $76.10  
  7 purchase totals = $825.08       $871.0698   $871.06   $871.05   $871.10