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 $125.51   13.620%   $142.6045   $142.60   $142.60   $142.60  
  Purchase #2 $234.71   9.647%   $257.3525   $257.35   $257.35   $257.40  
  Purchase #3 $166.80   8.686%   $181.2882   $181.29   $181.30   $181.30  
  Purchase #4 $56.36   4.248%   $58.7542   $58.75   $58.75   $58.80  
  Purchase #5 $153.87   12.186%   $172.6206   $172.62   $172.60   $172.60  
  Purchase #6 $120.72   5.629%   $127.5153   $127.52   $127.50   $127.50  
  Purchase #7 $26.55   9.551%   $29.0858   $29.09   $29.10   $29.10  
  7 purchase totals = $884.52       $969.2211   $969.22   $969.20   $969.30