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 $62.43   9.193%   $68.1692   $68.17   $68.15   $68.20  
  Purchase #2 $134.87   8.847%   $146.8019   $146.80   $146.80   $146.80  
  Purchase #3 $95.27   11.685%   $106.4023   $106.40   $106.40   $106.40  
  Purchase #4 $249.77   9.150%   $272.624   $272.62   $272.60   $272.60  
  Purchase #5 $237.49   8.529%   $257.7455   $257.75   $257.75   $257.70  
  Purchase #6 $220.62   6.541%   $235.0508   $235.05   $235.05   $235.10  
  Purchase #7 $227.34   11.839%   $254.2548   $254.25   $254.25   $254.30  
  7 purchase totals = $1,227.79       $1,341.0485   $1,341.04   $1,341.00   $1,341.10