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 $47.98   13.163%   $54.2956   $54.30   $54.30   $54.30  
  Purchase #2 $125.32   3.664%   $129.9117   $129.91   $129.90   $129.90  
  Purchase #3 $198.89   7.328%   $213.4647   $213.46   $213.45   $213.50  
  Purchase #4 $216.65   4.786%   $227.0189   $227.02   $227.00   $227.00  
  Purchase #5 $219.91   3.264%   $227.0879   $227.09   $227.10   $227.10  
  Purchase #6 $222.94   10.607%   $246.5872   $246.59   $246.60   $246.60  
  Purchase #7 $92.36   11.462%   $102.9463   $102.95   $102.95   $102.90  
  7 purchase totals = $1,124.05       $1,201.3123   $1,201.32   $1,201.30   $1,201.30