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 $64.49   7.238%   $69.1578   $69.16   $69.15   $69.20  
  Purchase #2 $24.81   3.729%   $25.7352   $25.74   $25.75   $25.70  
  Purchase #3 $149.92   12.723%   $168.9943   $168.99   $169.00   $169.00  
  Purchase #4 $238.83   5.253%   $251.3757   $251.38   $251.40   $251.40  
  Purchase #5 $161.42   6.670%   $172.1867   $172.19   $172.20   $172.20  
  Purchase #6 $151.63   13.298%   $171.7938   $171.79   $171.80   $171.80  
  Purchase #7 $129.94   11.642%   $145.0676   $145.07   $145.05   $145.10  
  7 purchase totals = $921.04       $1,004.3111   $1,004.32   $1,004.35   $1,004.40