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 $111.39   11.569%   $124.2767   $124.28   $124.30   $124.30  
  Purchase #2 $73.62   4.656%   $77.0477   $77.05   $77.05   $77.00  
  Purchase #3 $250.86   7.524%   $269.7347   $269.73   $269.75   $269.70  
  Purchase #4 $149.46   3.764%   $155.0857   $155.09   $155.10   $155.10  
  Purchase #5 $125.32   12.163%   $140.5627   $140.56   $140.55   $140.60  
  Purchase #6 $118.30   8.168%   $127.9627   $127.96   $127.95   $128.00  
  Purchase #7 $152.91   3.605%   $158.4224   $158.42   $158.40   $158.40  
  7 purchase totals = $981.86       $1,053.0926   $1,053.09   $1,053.10   $1,053.10