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 $115.57   7.526%   $124.2678   $124.27   $124.25   $124.30  
  Purchase #2 $181.31   6.359%   $192.8395   $192.84   $192.85   $192.80  
  Purchase #3 $121.37   7.727%   $130.7483   $130.75   $130.75   $130.70  
  Purchase #4 $76.50   11.284%   $85.1323   $85.13   $85.15   $85.10  
  Purchase #5 $186.80   13.323%   $211.6874   $211.69   $211.70   $211.70  
  Purchase #6 $165.96   3.610%   $171.9512   $171.95   $171.95   $172.00  
  Purchase #7 $127.92   3.408%   $132.2795   $132.28   $132.30   $132.30  
  7 purchase totals = $975.43       $1,048.9060   $1,048.91   $1,048.95   $1,048.90