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 $167.39   9.452%   $183.2117   $183.21   $183.20   $183.20  
  Purchase #2 $30.68   12.365%   $34.4736   $34.47   $34.45   $34.50  
  Purchase #3 $120.45   6.152%   $127.8601   $127.86   $127.85   $127.90  
  Purchase #4 $61.70   4.710%   $64.6061   $64.61   $64.60   $64.60  
  Purchase #5 $228.78   9.120%   $249.6447   $249.64   $249.65   $249.60  
  Purchase #6 $174.44   11.229%   $194.0279   $194.03   $194.05   $194.00  
  Purchase #7 $204.30   13.649%   $232.1849   $232.18   $232.20   $232.20  
  7 purchase totals = $987.74       $1,086.0090   $1,086.00   $1,086.00   $1,086.00