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 $182.53   10.383%   $201.4821   $201.48   $201.50   $201.50  
  Purchase #2 $202.96   12.157%   $227.6338   $227.63   $227.65   $227.60  
  Purchase #3 $28.49   4.490%   $29.7692   $29.77   $29.75   $29.80  
  Purchase #4 $159.69   4.715%   $167.2194   $167.22   $167.20   $167.20  
  Purchase #5 $95.31   6.181%   $101.2011   $101.20   $101.20   $101.20  
  Purchase #6 $135.90   3.258%   $140.3276   $140.33   $140.35   $140.30  
  Purchase #7 $156.75   13.208%   $177.4535   $177.45   $177.45   $177.50  
  7 purchase totals = $961.63       $1,045.0867   $1,045.08   $1,045.10   $1,045.10