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 $59.91   3.458%   $61.9817   $61.98   $62.00   $62.00  
  Purchase #2 $199.68   6.527%   $212.7131   $212.71   $212.70   $212.70  
  Purchase #3 $96.62   11.258%   $107.4975   $107.50   $107.50   $107.50  
  Purchase #4 $135.53   5.754%   $143.3284   $143.33   $143.35   $143.30  
  Purchase #5 $90.75   12.658%   $102.2371   $102.24   $102.25   $102.20  
  Purchase #6 $124.57   4.798%   $130.5469   $130.55   $130.55   $130.50  
  Purchase #7 $31.95   9.177%   $34.8821   $34.88   $34.90   $34.90  
  7 purchase totals = $739.01       $793.1868   $793.19   $793.25   $793.10