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 $38.77   12.631%   $43.667   $43.67   $43.65   $43.70  
  Purchase #2 $199.87   5.544%   $210.9508   $210.95   $210.95   $211.00  
  Purchase #3 $190.28   4.298%   $198.4582   $198.46   $198.45   $198.50  
  Purchase #4 $91.83   6.102%   $97.4335   $97.43   $97.45   $97.40  
  Purchase #5 $192.74   3.456%   $199.4011   $199.40   $199.40   $199.40  
  Purchase #6 $26.66   8.207%   $28.848   $28.85   $28.85   $28.80  
  Purchase #7 $232.82   8.549%   $252.7238   $252.72   $252.70   $252.70  
  7 purchase totals = $972.97       $1,031.4824   $1,031.48   $1,031.45   $1,031.50