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 $42.91   8.762%   $46.6698   $46.67   $46.65   $46.70  
  Purchase #2 $203.75   3.136%   $210.1396   $210.14   $210.15   $210.10  
  Purchase #3 $88.66   7.343%   $95.1703   $95.17   $95.15   $95.20  
  Purchase #4 $157.40   3.122%   $162.314   $162.31   $162.30   $162.30  
  Purchase #5 $118.44   4.313%   $123.5483   $123.55   $123.55   $123.50  
  Purchase #6 $197.29   5.826%   $208.7841   $208.78   $208.80   $208.80  
  Purchase #7 $189.66   8.464%   $205.7128   $205.71   $205.70   $205.70  
  7 purchase totals = $998.11       $1,052.3389   $1,052.33   $1,052.30   $1,052.30