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 $36.78   12.288%   $41.2995   $41.30   $41.30   $41.30  
  Purchase #2 $208.25   10.288%   $229.6748   $229.67   $229.65   $229.70  
  Purchase #3 $56.98   6.841%   $60.878   $60.88   $60.90   $60.90  
  Purchase #4 $127.49   7.267%   $136.7547   $136.75   $136.75   $136.80  
  Purchase #5 $250.64   13.205%   $283.737   $283.74   $283.75   $283.70  
  Purchase #6 $221.77   13.851%   $252.4874   $252.49   $252.50   $252.50  
  Purchase #7 $225.66   10.717%   $249.844   $249.84   $249.85   $249.80  
  7 purchase totals = $1,127.57       $1,254.6754   $1,254.67   $1,254.70   $1,254.70