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 $239.80   6.727%   $255.9313   $255.93   $255.95   $255.90  
  Purchase #2 $166.29   10.151%   $183.1701   $183.17   $183.15   $183.20  
  Purchase #3 $211.59   5.134%   $222.453   $222.45   $222.45   $222.50  
  Purchase #4 $68.77   6.590%   $73.3019   $73.30   $73.30   $73.30  
  Purchase #5 $66.67   6.164%   $70.7795   $70.78   $70.80   $70.80  
  Purchase #6 $106.94   12.701%   $120.5224   $120.52   $120.50   $120.50  
  Purchase #7 $169.30   11.150%   $188.177   $188.18   $188.20   $188.20  
  7 purchase totals = $1,029.36       $1,114.3352   $1,114.33   $1,114.35   $1,114.40