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 $68.85   10.452%   $76.0462   $76.05   $76.05   $76.00  
  Purchase #2 $147.36   7.442%   $158.3265   $158.33   $158.35   $158.30  
  Purchase #3 $132.76   3.804%   $137.8102   $137.81   $137.80   $137.80  
  Purchase #4 $109.74   13.471%   $124.5231   $124.52   $124.50   $124.50  
  Purchase #5 $25.40   9.199%   $27.7365   $27.74   $27.75   $27.70  
  Purchase #6 $175.78   8.784%   $191.2205   $191.22   $191.20   $191.20  
  Purchase #7 $69.32   12.442%   $77.9448   $77.94   $77.95   $77.90  
  7 purchase totals = $729.21       $793.6078   $793.61   $793.60   $793.40