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 $216.58   7.392%   $232.5896   $232.59   $232.60   $232.60  
  Purchase #2 $125.95   4.783%   $131.9742   $131.97   $131.95   $132.00  
  Purchase #3 $118.28   6.510%   $125.98   $125.98   $126.00   $126.00  
  Purchase #4 $210.71   5.779%   $222.8869   $222.89   $222.90   $222.90  
  Purchase #5 $51.93   6.780%   $55.4509   $55.45   $55.45   $55.50  
  Purchase #6 $223.91   10.200%   $246.7488   $246.75   $246.75   $246.70  
  Purchase #7 $110.41   3.441%   $114.2092   $114.21   $114.20   $114.20  
  7 purchase totals = $1,057.77       $1,129.8396   $1,129.84   $1,129.85   $1,129.90