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 $63.45   9.255%   $69.3223   $69.32   $69.30   $69.30  
  Purchase #2 $115.80   7.641%   $124.6483   $124.65   $124.65   $124.60  
  Purchase #3 $159.63   4.588%   $166.9538   $166.95   $166.95   $167.00  
  Purchase #4 $36.51   8.415%   $39.5823   $39.58   $39.60   $39.60  
  Purchase #5 $29.56   8.243%   $31.9966   $32.00   $32.00   $32.00  
  Purchase #6 $228.31   3.813%   $237.0155   $237.02   $237.00   $237.00  
  Purchase #7 $126.31   13.592%   $143.4781   $143.48   $143.50   $143.50  
  7 purchase totals = $759.57       $812.9969   $813.00   $813.00   $813.00