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 $212.95   5.287%   $224.2087   $224.21   $224.20   $224.20  
  Purchase #2 $40.39   13.198%   $45.7207   $45.72   $45.70   $45.70  
  Purchase #3 $69.69   8.681%   $75.7398   $75.74   $75.75   $75.70  
  Purchase #4 $176.76   11.546%   $197.1687   $197.17   $197.15   $197.20  
  Purchase #5 $233.82   6.215%   $248.3519   $248.35   $248.35   $248.40  
  Purchase #6 $167.52   8.149%   $181.1712   $181.17   $181.15   $181.20  
  Purchase #7 $249.49   7.680%   $268.6508   $268.65   $268.65   $268.70  
  7 purchase totals = $1,150.62       $1,241.0118   $1,241.01   $1,240.95   $1,241.10