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 $161.34   10.283%   $177.9306   $177.93   $177.95   $177.90  
  Purchase #2 $23.92   13.233%   $27.0853   $27.09   $27.10   $27.10  
  Purchase #3 $135.80   11.123%   $150.905   $150.91   $150.90   $150.90  
  Purchase #4 $213.38   5.415%   $224.9345   $224.93   $224.95   $224.90  
  Purchase #5 $93.38   8.503%   $101.3201   $101.32   $101.30   $101.30  
  Purchase #6 $145.76   11.144%   $162.0035   $162.00   $162.00   $162.00  
  Purchase #7 $223.53   11.758%   $249.8127   $249.81   $249.80   $249.80  
  7 purchase totals = $997.11       $1,093.9917   $1,093.99   $1,094.00   $1,093.90