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 $52.74   12.819%   $59.5007   $59.50   $59.50   $59.50  
  Purchase #2 $164.84   4.137%   $171.6594   $171.66   $171.65   $171.70  
  Purchase #3 $140.25   5.524%   $147.9974   $148.00   $148.00   $148.00  
  Purchase #4 $242.33   12.294%   $272.1221   $272.12   $272.10   $272.10  
  Purchase #5 $45.41   9.163%   $49.5709   $49.57   $49.55   $49.60  
  Purchase #6 $248.98   7.214%   $266.9414   $266.94   $266.95   $266.90  
  Purchase #7 $134.25   11.396%   $149.5491   $149.55   $149.55   $149.50  
  7 purchase totals = $1,028.80       $1,117.3410   $1,117.34   $1,117.30   $1,117.30