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 $149.63   10.720%   $165.6703   $165.67   $165.65   $165.70  
  Purchase #2 $82.88   9.809%   $91.0097   $91.01   $91.00   $91.00  
  Purchase #3 $70.30   9.137%   $76.7233   $76.72   $76.70   $76.70  
  Purchase #4 $109.94   4.171%   $114.5256   $114.53   $114.55   $114.50  
  Purchase #5 $69.36   3.601%   $71.8577   $71.86   $71.85   $71.90  
  Purchase #6 $168.69   3.739%   $174.9973   $175.00   $175.00   $175.00  
  Purchase #7 $60.54   11.676%   $67.6087   $67.61   $67.60   $67.60  
  7 purchase totals = $711.34       $762.3926   $762.40   $762.35   $762.40