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 $247.69   8.862%   $269.6403   $269.64   $269.65   $269.60  
  Purchase #2 $196.99   6.807%   $210.3991   $210.40   $210.40   $210.40  
  Purchase #3 $28.83   8.745%   $31.3512   $31.35   $31.35   $31.40  
  Purchase #4 $168.41   9.551%   $184.4948   $184.49   $184.50   $184.50  
  Purchase #5 $193.34   5.421%   $203.821   $203.82   $203.80   $203.80  
  Purchase #6 $24.26   4.585%   $25.3723   $25.37   $25.35   $25.40  
  Purchase #7 $90.73   9.265%   $99.1361   $99.14   $99.15   $99.10  
  7 purchase totals = $950.25       $1,024.2148   $1,024.21   $1,024.20   $1,024.20