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 $186.62   9.355%   $204.0783   $204.08   $204.10   $204.10  
  Purchase #2 $116.39   8.238%   $125.9782   $125.98   $126.00   $126.00  
  Purchase #3 $209.62   10.670%   $231.9865   $231.99   $232.00   $232.00  
  Purchase #4 $44.42   5.809%   $47.0004   $47.00   $47.00   $47.00  
  Purchase #5 $221.88   10.461%   $245.0909   $245.09   $245.10   $245.10  
  Purchase #6 $119.59   4.158%   $124.5626   $124.56   $124.55   $124.60  
  Purchase #7 $243.42   5.721%   $257.3461   $257.35   $257.35   $257.30  
  7 purchase totals = $1,141.94       $1,236.0430   $1,236.05   $1,236.10   $1,236.10