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 $207.68   12.462%   $233.5611   $233.56   $233.55   $233.60  
  Purchase #2 $230.83   3.403%   $238.6851   $238.69   $238.70   $238.70  
  Purchase #3 $140.96   9.854%   $154.8502   $154.85   $154.85   $154.90  
  Purchase #4 $31.69   8.414%   $34.3564   $34.36   $34.35   $34.40  
  Purchase #5 $120.81   12.399%   $135.7892   $135.79   $135.80   $135.80  
  Purchase #6 $140.54   3.700%   $145.74   $145.74   $145.75   $145.70  
  Purchase #7 $78.90   3.379%   $81.566   $81.57   $81.55   $81.60  
  7 purchase totals = $951.41       $1,024.5480   $1,024.56   $1,024.55   $1,024.70