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 $180.25   12.843%   $203.3995   $203.40   $203.40   $203.40  
  Purchase #2 $25.49   3.364%   $26.3475   $26.35   $26.35   $26.30  
  Purchase #3 $102.81   3.783%   $106.6993   $106.70   $106.70   $106.70  
  Purchase #4 $202.85   9.222%   $221.5568   $221.56   $221.55   $221.60  
  Purchase #5 $66.28   10.175%   $73.024   $73.02   $73.00   $73.00  
  Purchase #6 $204.90   11.480%   $228.4225   $228.42   $228.40   $228.40  
  Purchase #7 $214.33   5.506%   $226.131   $226.13   $226.15   $226.10  
  7 purchase totals = $996.91       $1,085.5806   $1,085.58   $1,085.55   $1,085.50