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 $45.33   6.619%   $48.3304   $48.33   $48.35   $48.30  
  Purchase #2 $167.48   9.588%   $183.538   $183.54   $183.55   $183.50  
  Purchase #3 $145.92   12.171%   $163.6799   $163.68   $163.70   $163.70  
  Purchase #4 $172.43   11.570%   $192.3802   $192.38   $192.40   $192.40  
  Purchase #5 $137.85   5.239%   $145.072   $145.07   $145.05   $145.10  
  Purchase #6 $6.34   6.203%   $6.7333   $6.73   $6.75   $6.70  
  Purchase #7 $214.52   10.796%   $237.6796   $237.68   $237.70   $237.70  
  7 purchase totals = $889.87       $977.4134   $977.41   $977.50   $977.40