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 $148.29   3.147%   $152.9567   $152.96   $152.95   $153.00  
  Purchase #2 $226.99   11.550%   $253.2073   $253.21   $253.20   $253.20  
  Purchase #3 $199.66   8.216%   $216.0641   $216.06   $216.05   $216.10  
  Purchase #4 $65.42   7.586%   $70.3828   $70.38   $70.40   $70.40  
  Purchase #5 $223.57   10.308%   $246.6156   $246.62   $246.60   $246.60  
  Purchase #6 $5.69   9.375%   $6.2234   $6.22   $6.20   $6.20  
  Purchase #7 $68.33   11.788%   $76.3847   $76.38   $76.40   $76.40  
  7 purchase totals = $937.95       $1,021.8346   $1,021.83   $1,021.80   $1,021.90