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 $72.92   6.272%   $77.4935   $77.49   $77.50   $77.50  
  Purchase #2 $118.52   8.509%   $128.6049   $128.60   $128.60   $128.60  
  Purchase #3 $201.81   5.180%   $212.2638   $212.26   $212.25   $212.30  
  Purchase #4 $94.32   6.769%   $100.7045   $100.70   $100.70   $100.70  
  Purchase #5 $239.84   7.258%   $257.2476   $257.25   $257.25   $257.20  
  Purchase #6 $27.27   9.137%   $29.7617   $29.76   $29.75   $29.80  
  Purchase #7 $228.36   9.535%   $250.1341   $250.13   $250.15   $250.10  
  7 purchase totals = $983.04       $1,056.2101   $1,056.19   $1,056.20   $1,056.20