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 $56.93   11.719%   $63.6016   $63.60   $63.60   $63.60  
  Purchase #2 $207.95   9.492%   $227.6886   $227.69   $227.70   $227.70  
  Purchase #3 $147.80   8.746%   $160.7266   $160.73   $160.75   $160.70  
  Purchase #4 $145.29   4.108%   $151.2585   $151.26   $151.25   $151.30  
  Purchase #5 $238.97   10.290%   $263.56   $263.56   $263.55   $263.60  
  Purchase #6 $88.61   4.158%   $92.2944   $92.29   $92.30   $92.30  
  Purchase #7 $221.58   6.377%   $235.7102   $235.71   $235.70   $235.70  
  7 purchase totals = $1,107.13       $1,194.8399   $1,194.84   $1,194.85   $1,194.90