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 $91.60   6.148%   $97.2316   $97.23   $97.25   $97.20  
  Purchase #2 $223.27   3.263%   $230.5553   $230.56   $230.55   $230.60  
  Purchase #3 $54.66   8.671%   $59.3996   $59.40   $59.40   $59.40  
  Purchase #4 $205.74   11.333%   $229.0565   $229.06   $229.05   $229.10  
  Purchase #5 $107.89   13.195%   $122.1261   $122.13   $122.15   $122.10  
  Purchase #6 $56.86   8.421%   $61.6482   $61.65   $61.65   $61.60  
  Purchase #7 $199.30   4.716%   $208.699   $208.70   $208.70   $208.70  
  7 purchase totals = $939.32       $1,008.7163   $1,008.73   $1,008.75   $1,008.70