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 $232.48   11.328%   $258.8153   $258.82   $258.80   $258.80  
  Purchase #2 $96.87   4.749%   $101.4704   $101.47   $101.45   $101.50  
  Purchase #3 $211.99   12.249%   $237.9567   $237.96   $237.95   $238.00  
  Purchase #4 $160.45   9.158%   $175.144   $175.14   $175.15   $175.10  
  Purchase #5 $16.81   11.245%   $18.7003   $18.70   $18.70   $18.70  
  Purchase #6 $97.60   13.597%   $110.8707   $110.87   $110.85   $110.90  
  Purchase #7 $202.78   3.801%   $210.4877   $210.49   $210.50   $210.50  
  7 purchase totals = $1,018.98       $1,113.4451   $1,113.45   $1,113.40   $1,113.50