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 $162.62   6.440%   $173.0927   $173.09   $173.10   $173.10  
  Purchase #2 $62.91   8.853%   $68.4794   $68.48   $68.50   $68.50  
  Purchase #3 $108.92   9.524%   $119.2935   $119.29   $119.30   $119.30  
  Purchase #4 $52.36   8.187%   $56.6467   $56.65   $56.65   $56.60  
  Purchase #5 $239.53   6.203%   $254.388   $254.39   $254.40   $254.40  
  Purchase #6 $179.90   6.120%   $190.9099   $190.91   $190.90   $190.90  
  Purchase #7 $141.70   8.324%   $153.4951   $153.50   $153.50   $153.50  
  7 purchase totals = $947.94       $1,016.3053   $1,016.31   $1,016.35   $1,016.30