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 $202.85   4.631%   $212.244   $212.24   $212.25   $212.20  
  Purchase #2 $49.81   13.867%   $56.7172   $56.72   $56.70   $56.70  
  Purchase #3 $126.89   8.161%   $137.2455   $137.25   $137.25   $137.20  
  Purchase #4 $144.32   7.464%   $155.092   $155.09   $155.10   $155.10  
  Purchase #5 $10.76   10.540%   $11.8941   $11.89   $11.90   $11.90  
  Purchase #6 $184.50   10.184%   $203.2895   $203.29   $203.30   $203.30  
  Purchase #7 $228.62   8.788%   $248.7111   $248.71   $248.70   $248.70  
  7 purchase totals = $947.75       $1,025.1934   $1,025.19   $1,025.20   $1,025.10