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 $233.27   9.222%   $254.7822   $254.78   $254.80   $254.80  
  Purchase #2 $74.71   11.542%   $83.333   $83.33   $83.35   $83.30  
  Purchase #3 $191.41   3.780%   $198.6453   $198.65   $198.65   $198.60  
  Purchase #4 $23.54   13.583%   $26.7374   $26.74   $26.75   $26.70  
  Purchase #5 $32.80   7.351%   $35.2111   $35.21   $35.20   $35.20  
  Purchase #6 $160.80   12.755%   $181.31   $181.31   $181.30   $181.30  
  Purchase #7 $206.73   3.523%   $214.0131   $214.01   $214.00   $214.00  
  7 purchase totals = $923.26       $994.0321   $994.03   $994.05   $993.90