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 $204.85   9.171%   $223.6368   $223.64   $223.65   $223.60  
  Purchase #2 $94.92   4.205%   $98.9114   $98.91   $98.90   $98.90  
  Purchase #3 $223.57   6.276%   $237.6013   $237.60   $237.60   $237.60  
  Purchase #4 $32.74   8.356%   $35.4758   $35.48   $35.50   $35.50  
  Purchase #5 $227.54   10.803%   $252.1211   $252.12   $252.10   $252.10  
  Purchase #6 $106.62   3.131%   $109.9583   $109.96   $109.95   $110.00  
  Purchase #7 $208.35   11.659%   $232.6415   $232.64   $232.65   $232.60  
  7 purchase totals = $1,098.59       $1,190.3462   $1,190.35   $1,190.35   $1,190.30