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 $232.59   13.432%   $263.8315   $263.83   $263.85   $263.80  
  Purchase #2 $163.97   5.840%   $173.5458   $173.55   $173.55   $173.50  
  Purchase #3 $38.40   9.419%   $42.0169   $42.02   $42.00   $42.00  
  Purchase #4 $11.49   12.818%   $12.9628   $12.96   $12.95   $13.00  
  Purchase #5 $207.36   3.816%   $215.2729   $215.27   $215.25   $215.30  
  Purchase #6 $192.50   4.619%   $201.3916   $201.39   $201.40   $201.40  
  Purchase #7 $37.93   13.465%   $43.0373   $43.04   $43.05   $43.00  
  7 purchase totals = $884.24       $952.0588   $952.06   $952.05   $952.00