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 $90.61   7.254%   $97.1828   $97.18   $97.20   $97.20  
  Purchase #2 $122.61   10.233%   $135.1567   $135.16   $135.15   $135.20  
  Purchase #3 $150.59   11.332%   $167.6549   $167.65   $167.65   $167.70  
  Purchase #4 $184.85   11.693%   $206.4645   $206.46   $206.45   $206.50  
  Purchase #5 $57.68   5.182%   $60.669   $60.67   $60.65   $60.70  
  Purchase #6 $137.89   6.799%   $147.2651   $147.27   $147.25   $147.30  
  Purchase #7 $207.51   10.477%   $229.2508   $229.25   $229.25   $229.30  
  7 purchase totals = $951.74       $1,043.6438   $1,043.64   $1,043.60   $1,043.90