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 $181.51   5.858%   $192.1429   $192.14   $192.15   $192.10  
  Purchase #2 $65.99   13.133%   $74.6565   $74.66   $74.65   $74.70  
  Purchase #3 $98.77   5.820%   $104.5184   $104.52   $104.50   $104.50  
  Purchase #4 $233.70   12.651%   $263.2654   $263.27   $263.25   $263.30  
  Purchase #5 $236.56   12.404%   $265.9029   $265.90   $265.90   $265.90  
  Purchase #6 $56.79   8.235%   $61.4667   $61.47   $61.45   $61.50  
  Purchase #7 $120.35   10.679%   $133.2022   $133.20   $133.20   $133.20  
  7 purchase totals = $993.67       $1,095.1550   $1,095.16   $1,095.10   $1,095.20