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 $54.57   10.425%   $60.2589   $60.26   $60.25   $60.30  
  Purchase #2 $113.51   11.157%   $126.1743   $126.17   $126.15   $126.20  
  Purchase #3 $111.28   12.400%   $125.0787   $125.08   $125.10   $125.10  
  Purchase #4 $64.76   13.335%   $73.3957   $73.40   $73.40   $73.40  
  Purchase #5 $102.77   4.736%   $107.6372   $107.64   $107.65   $107.60  
  Purchase #6 $36.72   8.708%   $39.9176   $39.92   $39.90   $39.90  
  Purchase #7 $75.66   8.662%   $82.2137   $82.21   $82.20   $82.20  
  7 purchase totals = $559.27       $614.6761   $614.68   $614.65   $614.70