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 $35.39   9.271%   $38.671   $38.67   $38.65   $38.70  
  Purchase #2 $249.25   9.275%   $272.3679   $272.37   $272.35   $272.40  
  Purchase #3 $186.26   13.273%   $210.9823   $210.98   $211.00   $211.00  
  Purchase #4 $49.46   5.462%   $52.1615   $52.16   $52.15   $52.20  
  Purchase #5 $81.65   10.151%   $89.9383   $89.94   $89.95   $89.90  
  Purchase #6 $89.28   4.220%   $93.0476   $93.05   $93.05   $93.00  
  Purchase #7 $203.56   5.266%   $214.2795   $214.28   $214.30   $214.30  
  7 purchase totals = $894.85       $971.4481   $971.45   $971.45   $971.50