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 $55.44   11.228%   $61.6648   $61.66   $61.65   $61.70  
  Purchase #2 $213.29   11.312%   $237.4174   $237.42   $237.40   $237.40  
  Purchase #3 $152.92   7.641%   $164.6046   $164.60   $164.60   $164.60  
  Purchase #4 $211.54   12.793%   $238.6023   $238.60   $238.60   $238.60  
  Purchase #5 $227.30   5.865%   $240.6311   $240.63   $240.65   $240.60  
  Purchase #6 $31.46   8.377%   $34.0954   $34.10   $34.10   $34.10  
  Purchase #7 $146.54   9.841%   $160.961   $160.96   $160.95   $161.00  
  7 purchase totals = $1,038.49       $1,137.9766   $1,137.97   $1,137.95   $1,138.00