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 $95.52   11.572%   $106.5736   $106.57   $106.55   $106.60  
  Purchase #2 $232.59   3.548%   $240.8423   $240.84   $240.85   $240.80  
  Purchase #3 $53.28   8.472%   $57.7939   $57.79   $57.80   $57.80  
  Purchase #4 $153.87   11.285%   $171.2342   $171.23   $171.25   $171.20  
  Purchase #5 $85.79   13.541%   $97.4068   $97.41   $97.40   $97.40  
  Purchase #6 $215.40   6.168%   $228.6859   $228.69   $228.70   $228.70  
  Purchase #7 $20.87   13.706%   $23.7304   $23.73   $23.75   $23.70  
  7 purchase totals = $857.32       $926.2671   $926.26   $926.30   $926.20