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 $228.75   10.283%   $252.2724   $252.27   $252.25   $252.30  
  Purchase #2 $206.95   9.107%   $225.7969   $225.80   $225.80   $225.80  
  Purchase #3 $110.50   3.731%   $114.6228   $114.62   $114.60   $114.60  
  Purchase #4 $156.91   5.205%   $165.0772   $165.08   $165.10   $165.10  
  Purchase #5 $183.66   7.714%   $197.8275   $197.83   $197.85   $197.80  
  Purchase #6 $153.70   5.212%   $161.7108   $161.71   $161.70   $161.70  
  Purchase #7 $167.73   13.226%   $189.914   $189.91   $189.90   $189.90  
  7 purchase totals = $1,208.20       $1,307.2216   $1,307.22   $1,307.20   $1,307.20