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 $188.68   4.821%   $197.7763   $197.78   $197.80   $197.80  
  Purchase #2 $132.37   11.242%   $147.251   $147.25   $147.25   $147.30  
  Purchase #3 $117.51   11.874%   $131.4631   $131.46   $131.45   $131.50  
  Purchase #4 $148.50   4.713%   $155.4988   $155.50   $155.50   $155.50  
  Purchase #5 $63.76   8.572%   $69.2255   $69.23   $69.25   $69.20  
  Purchase #6 $77.86   11.346%   $86.694   $86.69   $86.70   $86.70  
  Purchase #7 $55.29   4.820%   $57.955   $57.96   $57.95   $58.00  
  7 purchase totals = $783.97       $845.8637   $845.87   $845.90   $846.00