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 $47.96   7.723%   $51.664   $51.66   $51.65   $51.70  
  Purchase #2 $74.96   3.679%   $77.7178   $77.72   $77.70   $77.70  
  Purchase #3 $215.40   12.119%   $241.5043   $241.50   $241.50   $241.50  
  Purchase #4 $10.77   11.794%   $12.0402   $12.04   $12.05   $12.00  
  Purchase #5 $228.92   6.117%   $242.923   $242.92   $242.90   $242.90  
  Purchase #6 $173.56   4.302%   $181.0266   $181.03   $181.05   $181.00  
  Purchase #7 $239.77   3.774%   $248.8189   $248.82   $248.80   $248.80  
  7 purchase totals = $991.34       $1,055.6948   $1,055.69   $1,055.65   $1,055.60