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 $84.75   11.681%   $94.6496   $94.65   $94.65   $94.60  
  Purchase #2 $135.33   6.409%   $144.0033   $144.00   $144.00   $144.00  
  Purchase #3 $49.37   5.769%   $52.2182   $52.22   $52.20   $52.20  
  Purchase #4 $163.56   5.631%   $172.7701   $172.77   $172.75   $172.80  
  Purchase #5 $6.26   13.155%   $7.0835   $7.08   $7.10   $7.10  
  Purchase #6 $175.75   11.250%   $195.5219   $195.52   $195.50   $195.50  
  Purchase #7 $200.51   13.416%   $227.4104   $227.41   $227.40   $227.40  
  7 purchase totals = $815.53       $893.6570   $893.65   $893.60   $893.60