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 $54.33   7.791%   $58.5629   $58.56   $58.55   $58.60  
  Purchase #2 $123.93   10.458%   $136.8906   $136.89   $136.90   $136.90  
  Purchase #3 $39.57   6.548%   $42.161   $42.16   $42.15   $42.20  
  Purchase #4 $230.88   5.424%   $243.4029   $243.40   $243.40   $243.40  
  Purchase #5 $185.77   5.481%   $195.9521   $195.95   $195.95   $196.00  
  Purchase #6 $233.42   6.234%   $247.9714   $247.97   $247.95   $248.00  
  Purchase #7 $100.83   6.106%   $106.9867   $106.99   $107.00   $107.00  
  7 purchase totals = $968.73       $1,031.9276   $1,031.92   $1,031.90   $1,032.10