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 $54.78   7.106%   $58.6727   $58.67   $58.65   $58.70  
  Purchase #2 $225.79   12.217%   $253.3748   $253.37   $253.35   $253.40  
  Purchase #3 $114.75   12.779%   $129.4139   $129.41   $129.40   $129.40  
  Purchase #4 $206.81   11.848%   $231.3128   $231.31   $231.30   $231.30  
  Purchase #5 $46.81   7.632%   $50.3825   $50.38   $50.40   $50.40  
  Purchase #6 $167.85   4.731%   $175.791   $175.79   $175.80   $175.80  
  Purchase #7 $172.44   8.489%   $187.0784   $187.08   $187.10   $187.10  
  7 purchase totals = $989.23       $1,086.0261   $1,086.01   $1,086.00   $1,086.10