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 $183.48   8.284%   $198.6795   $198.68   $198.70   $198.70  
  Purchase #2 $219.88   8.714%   $239.0403   $239.04   $239.05   $239.00  
  Purchase #3 $220.32   12.546%   $247.9613   $247.96   $247.95   $248.00  
  Purchase #4 $44.97   12.842%   $50.745   $50.75   $50.75   $50.70  
  Purchase #5 $95.33   10.302%   $105.1509   $105.15   $105.15   $105.20  
  Purchase #6 $33.44   9.736%   $36.6957   $36.70   $36.70   $36.70  
  Purchase #7 $199.61   11.836%   $223.2358   $223.24   $223.25   $223.20  
  7 purchase totals = $997.03       $1,101.5085   $1,101.52   $1,101.55   $1,101.50