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 $63.85   6.784%   $68.1816   $68.18   $68.20   $68.20  
  Purchase #2 $164.42   11.450%   $183.2461   $183.25   $183.25   $183.20  
  Purchase #3 $154.77   12.634%   $174.3236   $174.32   $174.30   $174.30  
  Purchase #4 $148.78   8.642%   $161.6376   $161.64   $161.65   $161.60  
  Purchase #5 $230.91   13.258%   $261.524   $261.52   $261.50   $261.50  
  Purchase #6 $38.53   12.450%   $43.327   $43.33   $43.35   $43.30  
  Purchase #7 $233.70   9.499%   $255.8992   $255.90   $255.90   $255.90  
  7 purchase totals = $1,034.96       $1,148.1391   $1,148.14   $1,148.15   $1,148.00