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 $24.98   3.476%   $25.8483   $25.85   $25.85   $25.80  
  Purchase #2 $37.41   10.143%   $41.2045   $41.20   $41.20   $41.20  
  Purchase #3 $58.40   7.270%   $62.6457   $62.65   $62.65   $62.60  
  Purchase #4 $112.58   9.143%   $122.8732   $122.87   $122.85   $122.90  
  Purchase #5 $44.62   9.155%   $48.705   $48.71   $48.70   $48.70  
  Purchase #6 $172.54   8.683%   $187.5216   $187.52   $187.50   $187.50  
  Purchase #7 $196.54   3.536%   $203.4897   $203.49   $203.50   $203.50  
  7 purchase totals = $647.07       $692.2880   $692.29   $692.25   $692.20