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 $53.69   12.431%   $60.3642   $60.36   $60.35   $60.40  
  Purchase #2 $181.60   8.367%   $196.7945   $196.79   $196.80   $196.80  
  Purchase #3 $136.34   5.771%   $144.2082   $144.21   $144.20   $144.20  
  Purchase #4 $55.38   4.459%   $57.8494   $57.85   $57.85   $57.80  
  Purchase #5 $120.75   8.578%   $131.1079   $131.11   $131.10   $131.10  
  Purchase #6 $192.82   9.739%   $211.5987   $211.60   $211.60   $211.60  
  Purchase #7 $234.60   3.433%   $242.6538   $242.65   $242.65   $242.70  
  7 purchase totals = $975.18       $1,044.5767   $1,044.57   $1,044.55   $1,044.60