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 $59.51   6.286%   $63.2508   $63.25   $63.25   $63.30  
  Purchase #2 $170.81   8.831%   $185.8942   $185.89   $185.90   $185.90  
  Purchase #3 $12.44   12.341%   $13.9752   $13.98   $14.00   $14.00  
  Purchase #4 $240.34   3.325%   $248.3313   $248.33   $248.35   $248.30  
  Purchase #5 $116.29   5.539%   $122.7313   $122.73   $122.75   $122.70  
  Purchase #6 $187.72   3.164%   $193.6595   $193.66   $193.65   $193.70  
  Purchase #7 $222.67   10.477%   $245.9991   $246.00   $246.00   $246.00  
  7 purchase totals = $1,009.78       $1,073.8414   $1,073.84   $1,073.90   $1,073.90