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 $136.82   11.600%   $152.6911   $152.69   $152.70   $152.70  
  Purchase #2 $145.92   11.249%   $162.3345   $162.33   $162.35   $162.30  
  Purchase #3 $226.41   4.350%   $236.2588   $236.26   $236.25   $236.30  
  Purchase #4 $88.56   7.368%   $95.0851   $95.09   $95.10   $95.10  
  Purchase #5 $192.70   4.159%   $200.7144   $200.71   $200.70   $200.70  
  Purchase #6 $50.72   11.699%   $56.6537   $56.65   $56.65   $56.70  
  Purchase #7 $118.61   10.515%   $131.0818   $131.08   $131.10   $131.10  
  7 purchase totals = $959.74       $1,034.8194   $1,034.81   $1,034.85   $1,034.90