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 $103.41   13.867%   $117.7499   $117.75   $117.75   $117.70  
  Purchase #2 $175.85   5.367%   $185.2879   $185.29   $185.30   $185.30  
  Purchase #3 $202.37   10.682%   $223.9872   $223.99   $224.00   $224.00  
  Purchase #4 $239.48   10.805%   $265.3558   $265.36   $265.35   $265.40  
  Purchase #5 $232.77   9.333%   $254.4944   $254.49   $254.50   $254.50  
  Purchase #6 $19.49   11.806%   $21.791   $21.79   $21.80   $21.80  
  Purchase #7 $166.95   13.515%   $189.5133   $189.51   $189.50   $189.50  
  7 purchase totals = $1,140.32       $1,258.1795   $1,258.18   $1,258.20   $1,258.20