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 $76.36   8.218%   $82.6353   $82.64   $82.65   $82.60  
  Purchase #2 $165.75   10.296%   $182.8156   $182.82   $182.80   $182.80  
  Purchase #3 $198.51   4.474%   $207.3913   $207.39   $207.40   $207.40  
  Purchase #4 $167.27   13.470%   $189.8013   $189.80   $189.80   $189.80  
  Purchase #5 $239.41   13.118%   $270.8158   $270.82   $270.80   $270.80  
  Purchase #6 $201.78   8.793%   $219.5225   $219.52   $219.50   $219.50  
  Purchase #7 $129.98   11.386%   $144.7795   $144.78   $144.80   $144.80  
  7 purchase totals = $1,179.06       $1,297.7613   $1,297.77   $1,297.75   $1,297.70