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 $140.98   13.776%   $160.4014   $160.40   $160.40   $160.40  
  Purchase #2 $191.26   5.601%   $201.9725   $201.97   $201.95   $202.00  
  Purchase #3 $49.96   5.458%   $52.6868   $52.69   $52.70   $52.70  
  Purchase #4 $246.34   8.123%   $266.3502   $266.35   $266.35   $266.40  
  Purchase #5 $126.75   6.587%   $135.099   $135.10   $135.10   $135.10  
  Purchase #6 $182.43   9.684%   $200.0965   $200.10   $200.10   $200.10  
  Purchase #7 $148.44   13.545%   $168.5462   $168.55   $168.55   $168.50  
  7 purchase totals = $1,086.16       $1,185.1526   $1,185.16   $1,185.15   $1,185.20