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 $122.96   10.237%   $135.5474   $135.55   $135.55   $135.50  
  Purchase #2 $106.27   9.325%   $116.1797   $116.18   $116.20   $116.20  
  Purchase #3 $249.43   6.793%   $266.3738   $266.37   $266.35   $266.40  
  Purchase #4 $24.67   7.416%   $26.4995   $26.50   $26.50   $26.50  
  Purchase #5 $203.99   10.217%   $224.8317   $224.83   $224.85   $224.80  
  Purchase #6 $162.70   11.249%   $181.0021   $181.00   $181.00   $181.00  
  Purchase #7 $68.90   6.432%   $73.3316   $73.33   $73.35   $73.30  
  7 purchase totals = $938.92       $1,023.7658   $1,023.76   $1,023.80   $1,023.70