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 $58.95   11.775%   $65.8914   $65.89   $65.90   $65.90  
  Purchase #2 $223.92   7.437%   $240.5729   $240.57   $240.55   $240.60  
  Purchase #3 $154.93   12.740%   $174.6681   $174.67   $174.65   $174.70  
  Purchase #4 $248.69   11.451%   $277.1675   $277.17   $277.15   $277.20  
  Purchase #5 $145.92   9.759%   $160.1603   $160.16   $160.15   $160.20  
  Purchase #6 $219.90   12.479%   $247.3413   $247.34   $247.35   $247.30  
  Purchase #7 $69.90   4.293%   $72.9008   $72.90   $72.90   $72.90  
  7 purchase totals = $1,122.21       $1,238.7023   $1,238.70   $1,238.65   $1,238.80