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 $224.34   13.222%   $254.0022   $254.00   $254.00   $254.00  
  Purchase #2 $184.36   11.381%   $205.342   $205.34   $205.35   $205.30  
  Purchase #3 $32.70   4.705%   $34.2385   $34.24   $34.25   $34.20  
  Purchase #4 $162.50   7.349%   $174.4421   $174.44   $174.45   $174.40  
  Purchase #5 $230.35   9.407%   $252.019   $252.02   $252.00   $252.00  
  Purchase #6 $141.98   12.144%   $159.2221   $159.22   $159.20   $159.20  
  Purchase #7 $109.40   7.274%   $117.3578   $117.36   $117.35   $117.40  
  7 purchase totals = $1,085.63       $1,196.6237   $1,196.62   $1,196.60   $1,196.50