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 $128.45   9.675%   $140.8775   $140.88   $140.90   $140.90  
  Purchase #2 $37.76   9.209%   $41.2373   $41.24   $41.25   $41.20  
  Purchase #3 $80.60   9.161%   $87.9838   $87.98   $88.00   $88.00  
  Purchase #4 $192.52   8.714%   $209.2962   $209.30   $209.30   $209.30  
  Purchase #5 $36.73   5.247%   $38.6572   $38.66   $38.65   $38.70  
  Purchase #6 $117.93   12.536%   $132.7137   $132.71   $132.70   $132.70  
  Purchase #7 $57.67   13.442%   $65.422   $65.42   $65.40   $65.40  
  7 purchase totals = $651.66       $716.1877   $716.19   $716.20   $716.20