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 $135.27   12.364%   $151.9948   $151.99   $152.00   $152.00  
  Purchase #2 $116.65   7.757%   $125.6985   $125.70   $125.70   $125.70  
  Purchase #3 $204.86   13.694%   $232.9135   $232.91   $232.90   $232.90  
  Purchase #4 $90.43   6.461%   $96.2727   $96.27   $96.25   $96.30  
  Purchase #5 $109.91   13.115%   $124.3247   $124.32   $124.30   $124.30  
  Purchase #6 $50.28   4.118%   $52.3505   $52.35   $52.35   $52.40  
  Purchase #7 $44.39   4.791%   $46.5167   $46.52   $46.50   $46.50  
  7 purchase totals = $751.79       $830.0714   $830.06   $830.00   $830.10