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 $54.96   12.464%   $61.8102   $61.81   $61.80   $61.80  
  Purchase #2 $163.89   9.419%   $179.3268   $179.33   $179.35   $179.30  
  Purchase #3 $235.40   13.175%   $266.414   $266.41   $266.40   $266.40  
  Purchase #4 $238.31   7.657%   $256.5574   $256.56   $256.55   $256.60  
  Purchase #5 $181.51   7.432%   $194.9998   $195.00   $195.00   $195.00  
  Purchase #6 $147.34   13.122%   $166.674   $166.67   $166.65   $166.70  
  Purchase #7 $215.61   11.163%   $239.6785   $239.68   $239.70   $239.70  
  7 purchase totals = $1,237.02       $1,365.4607   $1,365.46   $1,365.45   $1,365.50