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 $74.66   11.158%   $82.9906   $82.99   $83.00   $83.00  
  Purchase #2 $153.32   7.199%   $164.3575   $164.36   $164.35   $164.40  
  Purchase #3 $182.41   3.815%   $189.3689   $189.37   $189.35   $189.40  
  Purchase #4 $231.74   11.187%   $257.6648   $257.66   $257.65   $257.70  
  Purchase #5 $5.67   6.436%   $6.0349   $6.03   $6.05   $6.00  
  Purchase #6 $123.88   12.664%   $139.5682   $139.57   $139.55   $139.60  
  Purchase #7 $12.27   6.199%   $13.0306   $13.03   $13.05   $13.00  
  7 purchase totals = $783.95       $853.0155   $853.01   $853.00   $853.10