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 $78.47   12.412%   $88.2097   $88.21   $88.20   $88.20  
  Purchase #2 $239.33   5.372%   $252.1868   $252.19   $252.20   $252.20  
  Purchase #3 $149.28   7.256%   $160.1118   $160.11   $160.10   $160.10  
  Purchase #4 $116.30   6.356%   $123.692   $123.69   $123.70   $123.70  
  Purchase #5 $44.35   11.397%   $49.4046   $49.40   $49.40   $49.40  
  Purchase #6 $67.94   4.481%   $70.9844   $70.98   $71.00   $71.00  
  Purchase #7 $99.43   3.599%   $103.0085   $103.01   $103.00   $103.00  
  7 purchase totals = $795.10       $847.5978   $847.59   $847.60   $847.60