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 $182.85   11.391%   $203.6784   $203.68   $203.70   $203.70  
  Purchase #2 $113.73   4.701%   $119.0764   $119.08   $119.10   $119.10  
  Purchase #3 $85.76   10.827%   $95.0452   $95.05   $95.05   $95.00  
  Purchase #4 $24.46   10.621%   $27.0579   $27.06   $27.05   $27.10  
  Purchase #5 $176.36   12.466%   $198.345   $198.35   $198.35   $198.30  
  Purchase #6 $132.57   3.586%   $137.324   $137.32   $137.30   $137.30  
  Purchase #7 $154.45   10.353%   $170.4402   $170.44   $170.45   $170.40  
  7 purchase totals = $870.18       $950.9671   $950.98   $951.00   $950.90