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 $53.78   5.239%   $56.5975   $56.60   $56.60   $56.60  
  Purchase #2 $132.65   11.791%   $148.2908   $148.29   $148.30   $148.30  
  Purchase #3 $175.60   9.385%   $192.0801   $192.08   $192.10   $192.10  
  Purchase #4 $241.37   11.700%   $269.6103   $269.61   $269.60   $269.60  
  Purchase #5 $119.77   9.325%   $130.9386   $130.94   $130.95   $130.90  
  Purchase #6 $233.38   13.647%   $265.2294   $265.23   $265.25   $265.20  
  Purchase #7 $190.27   6.473%   $202.5862   $202.59   $202.60   $202.60  
  7 purchase totals = $1,146.82       $1,265.3329   $1,265.34   $1,265.40   $1,265.30