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 $65.81   12.515%   $74.0461   $74.05   $74.05   $74.00  
  Purchase #2 $166.37   11.537%   $185.5641   $185.56   $185.55   $185.60  
  Purchase #3 $222.37   10.574%   $245.8834   $245.88   $245.90   $245.90  
  Purchase #4 $187.86   12.474%   $211.2937   $211.29   $211.30   $211.30  
  Purchase #5 $160.98   9.443%   $176.1813   $176.18   $176.20   $176.20  
  Purchase #6 $38.58   11.270%   $42.928   $42.93   $42.95   $42.90  
  Purchase #7 $120.88   10.103%   $133.0925   $133.09   $133.10   $133.10  
  7 purchase totals = $962.85       $1,068.9891   $1,068.98   $1,069.05   $1,069.00