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 $90.58   5.313%   $95.3925   $95.39   $95.40   $95.40  
  Purchase #2 $240.72   12.703%   $271.2987   $271.30   $271.30   $271.30  
  Purchase #3 $160.94   9.374%   $176.0265   $176.03   $176.05   $176.00  
  Purchase #4 $96.49   4.388%   $100.724   $100.72   $100.70   $100.70  
  Purchase #5 $152.51   10.629%   $168.7203   $168.72   $168.70   $168.70  
  Purchase #6 $132.79   3.554%   $137.5094   $137.51   $137.50   $137.50  
  Purchase #7 $174.68   3.591%   $180.9528   $180.95   $180.95   $181.00  
  7 purchase totals = $1,048.71       $1,130.6242   $1,130.62   $1,130.60   $1,130.60