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 $247.34   10.703%   $273.8128   $273.81   $273.80   $273.80  
  Purchase #2 $78.76   11.418%   $87.7528   $87.75   $87.75   $87.80  
  Purchase #3 $153.30   10.762%   $169.7981   $169.80   $169.80   $169.80  
  Purchase #4 $39.37   5.346%   $41.4747   $41.47   $41.45   $41.50  
  Purchase #5 $183.37   9.576%   $200.9295   $200.93   $200.95   $200.90  
  Purchase #6 $62.81   7.722%   $67.6602   $67.66   $67.65   $67.70  
  Purchase #7 $193.80   4.166%   $201.8737   $201.87   $201.85   $201.90  
  7 purchase totals = $958.75       $1,043.3018   $1,043.29   $1,043.25   $1,043.40