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 $113.67   4.270%   $118.5237   $118.52   $118.50   $118.50  
  Purchase #2 $201.36   3.221%   $207.8458   $207.85   $207.85   $207.80  
  Purchase #3 $179.48   4.764%   $188.0304   $188.03   $188.05   $188.00  
  Purchase #4 $77.69   10.241%   $85.6462   $85.65   $85.65   $85.60  
  Purchase #5 $88.66   9.448%   $97.0366   $97.04   $97.05   $97.00  
  Purchase #6 $229.70   9.144%   $250.7038   $250.70   $250.70   $250.70  
  Purchase #7 $238.50   5.114%   $250.6969   $250.70   $250.70   $250.70  
  7 purchase totals = $1,129.06       $1,198.4834   $1,198.49   $1,198.50   $1,198.30