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 $220.76   7.810%   $238.0014   $238.00   $238.00   $238.00  
  Purchase #2 $174.31   12.194%   $195.5654   $195.57   $195.55   $195.60  
  Purchase #3 $199.61   13.606%   $226.7689   $226.77   $226.75   $226.80  
  Purchase #4 $115.60   10.283%   $127.4871   $127.49   $127.50   $127.50  
  Purchase #5 $46.58   10.423%   $51.435   $51.44   $51.45   $51.40  
  Purchase #6 $115.56   6.266%   $122.801   $122.80   $122.80   $122.80  
  Purchase #7 $91.56   5.210%   $96.3303   $96.33   $96.35   $96.30  
  7 purchase totals = $963.98       $1,058.3891   $1,058.40   $1,058.40   $1,058.40