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 $211.31   10.623%   $233.7575   $233.76   $233.75   $233.80  
  Purchase #2 $52.50   8.157%   $56.7824   $56.78   $56.80   $56.80  
  Purchase #3 $110.99   5.113%   $116.6649   $116.66   $116.65   $116.70  
  Purchase #4 $239.38   9.660%   $262.5041   $262.50   $262.50   $262.50  
  Purchase #5 $246.65   5.158%   $259.3722   $259.37   $259.35   $259.40  
  Purchase #6 $83.84   11.320%   $93.3307   $93.33   $93.35   $93.30  
  Purchase #7 $243.55   13.689%   $276.8896   $276.89   $276.90   $276.90  
  7 purchase totals = $1,188.22       $1,299.3014   $1,299.29   $1,299.30   $1,299.40