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 $186.66   3.115%   $192.4745   $192.47   $192.45   $192.50  
  Purchase #2 $158.99   11.109%   $176.6522   $176.65   $176.65   $176.70  
  Purchase #3 $207.64   5.499%   $219.0581   $219.06   $219.05   $219.10  
  Purchase #4 $71.27   5.214%   $74.986   $74.99   $75.00   $75.00  
  Purchase #5 $12.97   6.337%   $13.7919   $13.79   $13.80   $13.80  
  Purchase #6 $57.39   11.733%   $64.1236   $64.12   $64.10   $64.10  
  Purchase #7 $92.93   4.836%   $97.4241   $97.42   $97.40   $97.40  
  7 purchase totals = $787.85       $838.5104   $838.50   $838.45   $838.60