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 $55.35   12.261%   $62.1365   $62.14   $62.15   $62.10  
  Purchase #2 $235.87   7.760%   $254.1735   $254.17   $254.15   $254.20  
  Purchase #3 $49.74   4.628%   $52.042   $52.04   $52.05   $52.00  
  Purchase #4 $248.81   3.168%   $256.6923   $256.69   $256.70   $256.70  
  Purchase #5 $8.87   7.362%   $9.523   $9.52   $9.50   $9.50  
  Purchase #6 $42.93   3.738%   $44.5347   $44.53   $44.55   $44.50  
  Purchase #7 $205.45   8.743%   $223.4125   $223.41   $223.40   $223.40  
  7 purchase totals = $847.02       $902.5145   $902.50   $902.50   $902.40