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 $158.45   5.745%   $167.553   $167.55   $167.55   $167.60  
  Purchase #2 $69.82   7.213%   $74.8561   $74.86   $74.85   $74.90  
  Purchase #3 $208.74   7.730%   $224.8756   $224.88   $224.90   $224.90  
  Purchase #4 $122.52   11.459%   $136.5596   $136.56   $136.55   $136.60  
  Purchase #5 $127.77   4.234%   $133.1798   $133.18   $133.20   $133.20  
  Purchase #6 $63.84   11.626%   $71.262   $71.26   $71.25   $71.30  
  Purchase #7 $243.57   3.613%   $252.3702   $252.37   $252.35   $252.40  
  7 purchase totals = $994.71       $1,060.6563   $1,060.66   $1,060.65   $1,060.90