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 $55.93   10.695%   $61.9117   $61.91   $61.90   $61.90  
  Purchase #2 $154.72   5.118%   $162.6386   $162.64   $162.65   $162.60  
  Purchase #3 $153.46   7.135%   $164.4094   $164.41   $164.40   $164.40  
  Purchase #4 $95.25   7.201%   $102.109   $102.11   $102.10   $102.10  
  Purchase #5 $125.58   5.476%   $132.4568   $132.46   $132.45   $132.50  
  Purchase #6 $214.55   11.398%   $239.0044   $239.00   $239.00   $239.00  
  Purchase #7 $161.96   11.648%   $180.8251   $180.83   $180.85   $180.80  
  7 purchase totals = $961.45       $1,043.3550   $1,043.36   $1,043.35   $1,043.30