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 $145.35   5.297%   $153.0492   $153.05   $153.05   $153.00  
  Purchase #2 $71.84   8.556%   $77.9866   $77.99   $78.00   $78.00  
  Purchase #3 $46.39   13.515%   $52.6596   $52.66   $52.65   $52.70  
  Purchase #4 $59.48   11.386%   $66.2524   $66.25   $66.25   $66.30  
  Purchase #5 $210.77   12.847%   $237.8476   $237.85   $237.85   $237.80  
  Purchase #6 $183.80   13.392%   $208.4145   $208.41   $208.40   $208.40  
  Purchase #7 $213.51   5.381%   $224.999   $225.00   $225.00   $225.00  
  7 purchase totals = $931.14       $1,021.2089   $1,021.21   $1,021.20   $1,021.20