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 $212.56   13.769%   $241.8274   $241.83   $241.85   $241.80  
  Purchase #2 $48.37   11.284%   $53.8281   $53.83   $53.85   $53.80  
  Purchase #3 $85.27   12.224%   $95.6934   $95.69   $95.70   $95.70  
  Purchase #4 $227.83   3.843%   $236.5855   $236.59   $236.60   $236.60  
  Purchase #5 $29.36   7.737%   $31.6316   $31.63   $31.65   $31.60  
  Purchase #6 $135.82   13.335%   $153.9316   $153.93   $153.95   $153.90  
  Purchase #7 $230.93   6.267%   $245.4024   $245.40   $245.40   $245.40  
  7 purchase totals = $970.14       $1,058.9000   $1,058.90   $1,059.00   $1,058.80