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 $60.69   8.767%   $66.0107   $66.01   $66.00   $66.00  
  Purchase #2 $233.85   8.109%   $252.8129   $252.81   $252.80   $252.80  
  Purchase #3 $203.52   7.579%   $218.9448   $218.94   $218.95   $218.90  
  Purchase #4 $21.38   12.769%   $24.11   $24.11   $24.10   $24.10  
  Purchase #5 $124.74   11.303%   $138.8394   $138.84   $138.85   $138.80  
  Purchase #6 $158.85   12.220%   $178.2615   $178.26   $178.25   $178.30  
  Purchase #7 $237.97   5.152%   $250.2302   $250.23   $250.25   $250.20  
  7 purchase totals = $1,041.00       $1,129.2095   $1,129.20   $1,129.20   $1,129.10