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 $232.35   13.699%   $264.1796   $264.18   $264.20   $264.20  
  Purchase #2 $86.88   10.239%   $95.7756   $95.78   $95.80   $95.80  
  Purchase #3 $186.27   12.873%   $210.2485   $210.25   $210.25   $210.20  
  Purchase #4 $34.33   7.585%   $36.9339   $36.93   $36.95   $36.90  
  Purchase #5 $180.68   4.706%   $189.1828   $189.18   $189.20   $189.20  
  Purchase #6 $136.62   12.518%   $153.7221   $153.72   $153.70   $153.70  
  Purchase #7 $120.54   4.320%   $125.7473   $125.75   $125.75   $125.70  
  7 purchase totals = $977.67       $1,075.7898   $1,075.79   $1,075.85   $1,075.70