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 $46.57   11.219%   $51.7947   $51.79   $51.80   $51.80  
  Purchase #2 $119.98   3.364%   $124.0161   $124.02   $124.00   $124.00  
  Purchase #3 $77.51   6.523%   $82.566   $82.57   $82.55   $82.60  
  Purchase #4 $24.32   8.535%   $26.3957   $26.40   $26.40   $26.40  
  Purchase #5 $224.56   7.319%   $240.9955   $241.00   $241.00   $241.00  
  Purchase #6 $61.76   6.189%   $65.5823   $65.58   $65.60   $65.60  
  Purchase #7 $107.55   3.459%   $111.2702   $111.27   $111.25   $111.30  
  7 purchase totals = $662.25       $702.6205   $702.63   $702.60   $702.70