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 $112.95   9.372%   $123.5357   $123.54   $123.55   $123.50  
  Purchase #2 $236.32   13.318%   $267.7931   $267.79   $267.80   $267.80  
  Purchase #3 $96.60   13.236%   $109.386   $109.39   $109.40   $109.40  
  Purchase #4 $186.82   10.702%   $206.8135   $206.81   $206.80   $206.80  
  Purchase #5 $64.93   7.283%   $69.6589   $69.66   $69.65   $69.70  
  Purchase #6 $151.48   9.467%   $165.8206   $165.82   $165.80   $165.80  
  Purchase #7 $163.39   8.547%   $177.3549   $177.35   $177.35   $177.40  
  7 purchase totals = $1,012.49       $1,120.3627   $1,120.36   $1,120.35   $1,120.40