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 $10.34   8.784%   $11.2483   $11.25   $11.25   $11.20  
  Purchase #2 $49.36   8.383%   $53.4978   $53.50   $53.50   $53.50  
  Purchase #3 $81.88   13.757%   $93.1442   $93.14   $93.15   $93.10  
  Purchase #4 $6.59   13.593%   $7.4858   $7.49   $7.50   $7.50  
  Purchase #5 $72.72   11.458%   $81.0523   $81.05   $81.05   $81.10  
  Purchase #6 $18.81   6.521%   $20.0366   $20.04   $20.05   $20.00  
  Purchase #7 $53.86   11.112%   $59.8449   $59.84   $59.85   $59.80  
  7 purchase totals = $293.56       $326.3099   $326.31   $326.35   $326.20