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 $165.84   10.159%   $182.6877   $182.69   $182.70   $182.70  
  Purchase #2 $205.31   11.398%   $228.7112   $228.71   $228.70   $228.70  
  Purchase #3 $23.68   12.188%   $26.5661   $26.57   $26.55   $26.60  
  Purchase #4 $75.73   7.342%   $81.2901   $81.29   $81.30   $81.30  
  Purchase #5 $152.51   10.462%   $168.4656   $168.47   $168.45   $168.50  
  Purchase #6 $226.88   11.232%   $252.3632   $252.36   $252.35   $252.40  
  Purchase #7 $161.51   10.850%   $179.0338   $179.03   $179.05   $179.00  
  7 purchase totals = $1,011.46       $1,119.1177   $1,119.12   $1,119.10   $1,119.20