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 $7.50   8.293%   $8.122   $8.12   $8.10   $8.10  
  Purchase #2 $123.48   11.815%   $138.0692   $138.07   $138.05   $138.10  
  Purchase #3 $231.99   4.855%   $243.2531   $243.25   $243.25   $243.30  
  Purchase #4 $185.32   11.729%   $207.0562   $207.06   $207.05   $207.10  
  Purchase #5 $147.49   6.521%   $157.1078   $157.11   $157.10   $157.10  
  Purchase #6 $221.43   8.335%   $239.8862   $239.89   $239.90   $239.90  
  Purchase #7 $128.35   5.352%   $135.2193   $135.22   $135.20   $135.20  
  7 purchase totals = $1,045.56       $1,128.7138   $1,128.72   $1,128.65   $1,128.80