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 $69.58   7.174%   $74.5717   $74.57   $74.55   $74.60  
  Purchase #2 $222.84   5.138%   $234.2895   $234.29   $234.30   $234.30  
  Purchase #3 $142.75   4.379%   $149.001   $149.00   $149.00   $149.00  
  Purchase #4 $93.66   4.125%   $97.5235   $97.52   $97.50   $97.50  
  Purchase #5 $233.56   3.702%   $242.2064   $242.21   $242.20   $242.20  
  Purchase #6 $30.77   10.722%   $34.0692   $34.07   $34.05   $34.10  
  Purchase #7 $147.31   5.558%   $155.4975   $155.50   $155.50   $155.50  
  7 purchase totals = $940.47       $987.1588   $987.16   $987.10   $987.20