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 $61.56   5.643%   $65.0338   $65.03   $65.05   $65.00  
  Purchase #2 $202.76   12.848%   $228.8106   $228.81   $228.80   $228.80  
  Purchase #3 $54.35   3.595%   $56.3039   $56.30   $56.30   $56.30  
  Purchase #4 $236.49   5.835%   $250.2892   $250.29   $250.30   $250.30  
  Purchase #5 $146.57   8.563%   $159.1208   $159.12   $159.10   $159.10  
  Purchase #6 $145.56   13.326%   $164.9573   $164.96   $164.95   $165.00  
  Purchase #7 $156.99   13.651%   $178.4207   $178.42   $178.40   $178.40  
  7 purchase totals = $1,004.28       $1,102.9363   $1,102.93   $1,102.90   $1,102.90