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 $49.51   8.527%   $53.7317   $53.73   $53.75   $53.70  
  Purchase #2 $232.72   11.205%   $258.7963   $258.80   $258.80   $258.80  
  Purchase #3 $24.60   5.763%   $26.0177   $26.02   $26.00   $26.00  
  Purchase #4 $139.50   9.643%   $152.952   $152.95   $152.95   $153.00  
  Purchase #5 $102.53   12.469%   $115.3145   $115.31   $115.30   $115.30  
  Purchase #6 $109.41   9.750%   $120.0775   $120.08   $120.10   $120.10  
  Purchase #7 $209.93   12.136%   $235.4071   $235.41   $235.40   $235.40  
  7 purchase totals = $868.20       $962.2968   $962.30   $962.30   $962.30