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 $95.73   7.184%   $102.6072   $102.61   $102.60   $102.60  
  Purchase #2 $131.97   3.745%   $136.9123   $136.91   $136.90   $136.90  
  Purchase #3 $71.90   12.163%   $80.6452   $80.65   $80.65   $80.60  
  Purchase #4 $220.79   4.735%   $231.2444   $231.24   $231.25   $231.20  
  Purchase #5 $130.49   4.171%   $135.9327   $135.93   $135.95   $135.90  
  Purchase #6 $186.52   8.515%   $202.4022   $202.40   $202.40   $202.40  
  Purchase #7 $123.34   11.337%   $137.3231   $137.32   $137.30   $137.30  
  7 purchase totals = $960.74       $1,027.0671   $1,027.06   $1,027.05   $1,026.90