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 $222.54   11.462%   $248.0475   $248.05   $248.05   $248.00  
  Purchase #2 $110.66   12.620%   $124.6253   $124.63   $124.65   $124.60  
  Purchase #3 $126.32   6.535%   $134.575   $134.58   $134.60   $134.60  
  Purchase #4 $217.58   6.334%   $231.3615   $231.36   $231.35   $231.40  
  Purchase #5 $145.30   4.231%   $151.4476   $151.45   $151.45   $151.40  
  Purchase #6 $201.52   10.561%   $222.8025   $222.80   $222.80   $222.80  
  Purchase #7 $114.82   4.604%   $120.1063   $120.11   $120.10   $120.10  
  7 purchase totals = $1,138.74       $1,232.9657   $1,232.98   $1,233.00   $1,232.90