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 $54.61   13.819%   $62.1566   $62.16   $62.15   $62.20  
  Purchase #2 $134.74   6.511%   $143.5129   $143.51   $143.50   $143.50  
  Purchase #3 $229.72   7.173%   $246.1978   $246.20   $246.20   $246.20  
  Purchase #4 $231.58   10.793%   $256.5744   $256.57   $256.55   $256.60  
  Purchase #5 $36.89   6.538%   $39.3019   $39.30   $39.30   $39.30  
  Purchase #6 $105.80   8.398%   $114.6851   $114.69   $114.70   $114.70  
  Purchase #7 $55.32   8.387%   $59.9597   $59.96   $59.95   $60.00  
  7 purchase totals = $848.66       $922.3884   $922.39   $922.35   $922.50