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 $134.84   13.622%   $153.2079   $153.21   $153.20   $153.20  
  Purchase #2 $177.36   13.535%   $201.3657   $201.37   $201.35   $201.40  
  Purchase #3 $16.77   3.847%   $17.4151   $17.42   $17.40   $17.40  
  Purchase #4 $59.57   5.157%   $62.642   $62.64   $62.65   $62.60  
  Purchase #5 $173.40   7.147%   $185.7929   $185.79   $185.80   $185.80  
  Purchase #6 $175.69   9.224%   $191.8956   $191.90   $191.90   $191.90  
  Purchase #7 $234.27   5.865%   $248.0099   $248.01   $248.00   $248.00  
  7 purchase totals = $971.90       $1,060.3291   $1,060.34   $1,060.30   $1,060.30