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 $25.44   5.382%   $26.8092   $26.81   $26.80   $26.80  
  Purchase #2 $92.60   6.121%   $98.268   $98.27   $98.25   $98.30  
  Purchase #3 $235.95   11.833%   $263.87   $263.87   $263.85   $263.90  
  Purchase #4 $181.92   6.378%   $193.5229   $193.52   $193.50   $193.50  
  Purchase #5 $158.83   3.655%   $164.6352   $164.64   $164.65   $164.60  
  Purchase #6 $238.72   7.257%   $256.0439   $256.04   $256.05   $256.00  
  Purchase #7 $44.63   3.634%   $46.2519   $46.25   $46.25   $46.30  
  7 purchase totals = $978.09       $1,049.4011   $1,049.40   $1,049.35   $1,049.40