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 $188.98   13.250%   $214.0199   $214.02   $214.00   $214.00  
  Purchase #2 $70.89   4.492%   $74.0744   $74.07   $74.05   $74.10  
  Purchase #3 $11.98   3.452%   $12.3935   $12.39   $12.40   $12.40  
  Purchase #4 $59.63   13.247%   $67.5292   $67.53   $67.55   $67.50  
  Purchase #5 $29.91   3.864%   $31.0657   $31.07   $31.05   $31.10  
  Purchase #6 $61.65   7.181%   $66.0771   $66.08   $66.10   $66.10  
  Purchase #7 $200.29   12.361%   $225.0478   $225.05   $225.05   $225.00  
  7 purchase totals = $623.33       $690.2076   $690.21   $690.20   $690.20