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 $12.26   3.444%   $12.6822   $12.68   $12.70   $12.70  
  Purchase #2 $53.52   6.288%   $56.8853   $56.89   $56.90   $56.90  
  Purchase #3 $148.76   7.684%   $160.1907   $160.19   $160.20   $160.20  
  Purchase #4 $26.39   11.331%   $29.3803   $29.38   $29.40   $29.40  
  Purchase #5 $101.43   4.292%   $105.7834   $105.78   $105.80   $105.80  
  Purchase #6 $115.78   11.640%   $129.2568   $129.26   $129.25   $129.30  
  Purchase #7 $141.30   9.194%   $154.2911   $154.29   $154.30   $154.30  
  7 purchase totals = $599.44       $648.4698   $648.47   $648.55   $648.60