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 $222.80   10.383%   $245.9333   $245.93   $245.95   $245.90  
  Purchase #2 $171.96   11.283%   $191.3622   $191.36   $191.35   $191.40  
  Purchase #3 $77.68   4.732%   $81.3558   $81.36   $81.35   $81.40  
  Purchase #4 $162.79   5.339%   $171.4814   $171.48   $171.50   $171.50  
  Purchase #5 $12.97   13.572%   $14.7303   $14.73   $14.75   $14.70  
  Purchase #6 $67.87   3.818%   $70.4613   $70.46   $70.45   $70.50  
  Purchase #7 $136.31   9.823%   $149.6997   $149.70   $149.70   $149.70  
  7 purchase totals = $852.38       $925.0240   $925.02   $925.05   $925.10