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 $47.41   13.679%   $53.8952   $53.90   $53.90   $53.90  
  Purchase #2 $24.81   5.281%   $26.1202   $26.12   $26.10   $26.10  
  Purchase #3 $204.78   3.844%   $212.6517   $212.65   $212.65   $212.70  
  Purchase #4 $176.39   5.632%   $186.3243   $186.32   $186.30   $186.30  
  Purchase #5 $170.74   6.181%   $181.2934   $181.29   $181.30   $181.30  
  Purchase #6 $237.80   6.116%   $252.3438   $252.34   $252.35   $252.30  
  Purchase #7 $138.85   4.632%   $145.2815   $145.28   $145.30   $145.30  
  7 purchase totals = $1,000.78       $1,057.9101   $1,057.90   $1,057.90   $1,057.90