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 $64.98   13.255%   $73.5931   $73.59   $73.60   $73.60  
  Purchase #2 $160.93   10.608%   $178.0015   $178.00   $178.00   $178.00  
  Purchase #3 $228.70   6.605%   $243.8056   $243.81   $243.80   $243.80  
  Purchase #4 $198.41   12.626%   $223.4612   $223.46   $223.45   $223.50  
  Purchase #5 $213.55   9.176%   $233.1453   $233.15   $233.15   $233.10  
  Purchase #6 $137.49   3.146%   $141.8154   $141.82   $141.80   $141.80  
  Purchase #7 $82.39   6.676%   $87.8904   $87.89   $87.90   $87.90  
  7 purchase totals = $1,086.45       $1,181.7125   $1,181.72   $1,181.70   $1,181.70