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 $204.39   10.551%   $225.9552   $225.96   $225.95   $226.00  
  Purchase #2 $61.28   7.578%   $65.9238   $65.92   $65.90   $65.90  
  Purchase #3 $118.96   6.257%   $126.4033   $126.40   $126.40   $126.40  
  Purchase #4 $181.71   8.466%   $197.0936   $197.09   $197.10   $197.10  
  Purchase #5 $187.82   10.625%   $207.7759   $207.78   $207.80   $207.80  
  Purchase #6 $190.81   9.203%   $208.3702   $208.37   $208.35   $208.40  
  Purchase #7 $18.95   12.157%   $21.2538   $21.25   $21.25   $21.30  
  7 purchase totals = $963.92       $1,052.7758   $1,052.77   $1,052.75   $1,052.90