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 $146.91   13.853%   $167.2614   $167.26   $167.25   $167.30  
  Purchase #2 $203.91   4.319%   $212.7169   $212.72   $212.70   $212.70  
  Purchase #3 $52.32   12.426%   $58.8213   $58.82   $58.80   $58.80  
  Purchase #4 $177.39   3.181%   $183.0328   $183.03   $183.05   $183.00  
  Purchase #5 $77.90   5.122%   $81.89   $81.89   $81.90   $81.90  
  Purchase #6 $210.50   7.741%   $226.7948   $226.79   $226.80   $226.80  
  Purchase #7 $11.41   9.436%   $12.4866   $12.49   $12.50   $12.50  
  7 purchase totals = $880.34       $943.0038   $943.00   $943.00   $943.00