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 $56.46   9.637%   $61.9011   $61.90   $61.90   $61.90  
  Purchase #2 $98.35   9.530%   $107.7228   $107.72   $107.70   $107.70  
  Purchase #3 $16.46   11.519%   $18.356   $18.36   $18.35   $18.40  
  Purchase #4 $74.65   4.220%   $77.8002   $77.80   $77.80   $77.80  
  Purchase #5 $86.57   10.667%   $95.8044   $95.80   $95.80   $95.80  
  Purchase #6 $190.32   11.385%   $211.9879   $211.99   $212.00   $212.00  
  Purchase #7 $19.25   6.713%   $20.5423   $20.54   $20.55   $20.50  
  7 purchase totals = $542.06       $594.1147   $594.11   $594.10   $594.10