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 $208.58   11.292%   $232.1329   $232.13   $232.15   $232.10  
  Purchase #2 $187.49   4.864%   $196.6095   $196.61   $196.60   $196.60  
  Purchase #3 $211.81   5.183%   $222.7881   $222.79   $222.80   $222.80  
  Purchase #4 $55.35   12.645%   $62.349   $62.35   $62.35   $62.30  
  Purchase #5 $27.34   6.274%   $29.0553   $29.06   $29.05   $29.10  
  Purchase #6 $71.49   13.798%   $81.3542   $81.35   $81.35   $81.40  
  Purchase #7 $101.32   5.142%   $106.5299   $106.53   $106.55   $106.50  
  7 purchase totals = $863.38       $930.8189   $930.82   $930.85   $930.80