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 $54.66   3.256%   $56.4397   $56.44   $56.45   $56.40  
  Purchase #2 $202.56   3.288%   $209.2202   $209.22   $209.20   $209.20  
  Purchase #3 $178.29   6.573%   $190.009   $190.01   $190.00   $190.00  
  Purchase #4 $244.38   6.476%   $260.206   $260.21   $260.20   $260.20  
  Purchase #5 $234.72   7.503%   $252.331   $252.33   $252.35   $252.30  
  Purchase #6 $38.66   6.621%   $41.2197   $41.22   $41.20   $41.20  
  Purchase #7 $36.56   10.854%   $40.5282   $40.53   $40.55   $40.50  
  7 purchase totals = $989.83       $1,049.9538   $1,049.96   $1,049.95   $1,049.80