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 $202.98   5.593%   $214.3327   $214.33   $214.35   $214.30  
  Purchase #2 $22.89   8.482%   $24.8315   $24.83   $24.85   $24.80  
  Purchase #3 $122.98   12.773%   $138.6882   $138.69   $138.70   $138.70  
  Purchase #4 $48.49   4.727%   $50.7821   $50.78   $50.80   $50.80  
  Purchase #5 $181.43   5.344%   $191.1256   $191.13   $191.15   $191.10  
  Purchase #6 $250.65   5.321%   $263.9871   $263.99   $264.00   $264.00  
  Purchase #7 $23.67   3.862%   $24.5841   $24.58   $24.60   $24.60  
  7 purchase totals = $853.09       $908.3313   $908.33   $908.45   $908.30