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 $164.30   13.266%   $186.096   $186.10   $186.10   $186.10  
  Purchase #2 $69.75   11.720%   $77.9247   $77.92   $77.90   $77.90  
  Purchase #3 $57.47   7.851%   $61.982   $61.98   $62.00   $62.00  
  Purchase #4 $191.79   5.690%   $202.7029   $202.70   $202.70   $202.70  
  Purchase #5 $178.30   3.424%   $184.405   $184.41   $184.40   $184.40  
  Purchase #6 $171.66   13.852%   $195.4383   $195.44   $195.45   $195.40  
  Purchase #7 $135.47   11.548%   $151.1141   $151.11   $151.10   $151.10  
  7 purchase totals = $968.74       $1,059.6630   $1,059.66   $1,059.65   $1,059.60