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 $73.67   11.344%   $82.0271   $82.03   $82.05   $82.00  
  Purchase #2 $174.77   11.668%   $195.1622   $195.16   $195.15   $195.20  
  Purchase #3 $140.44   5.317%   $147.9072   $147.91   $147.90   $147.90  
  Purchase #4 $29.26   12.843%   $33.0179   $33.02   $33.00   $33.00  
  Purchase #5 $230.95   11.158%   $256.7194   $256.72   $256.70   $256.70  
  Purchase #6 $36.97   11.644%   $41.2748   $41.27   $41.25   $41.30  
  Purchase #7 $244.79   5.538%   $258.3465   $258.35   $258.35   $258.30  
  7 purchase totals = $930.85       $1,014.4551   $1,014.46   $1,014.40   $1,014.40