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 $118.48   7.714%   $127.6195   $127.62   $127.60   $127.60  
  Purchase #2 $100.36   13.121%   $113.5282   $113.53   $113.55   $113.50  
  Purchase #3 $50.37   3.485%   $52.1254   $52.13   $52.15   $52.10  
  Purchase #4 $134.79   13.208%   $152.5931   $152.59   $152.60   $152.60  
  Purchase #5 $228.77   11.309%   $254.6416   $254.64   $254.65   $254.60  
  Purchase #6 $166.69   5.715%   $176.2163   $176.22   $176.20   $176.20  
  Purchase #7 $185.52   9.121%   $202.4413   $202.44   $202.45   $202.40  
  7 purchase totals = $984.98       $1,079.1654   $1,079.17   $1,079.20   $1,079.00