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 $141.43   13.813%   $160.9657   $160.97   $160.95   $161.00  
  Purchase #2 $69.53   5.413%   $73.2937   $73.29   $73.30   $73.30  
  Purchase #3 $91.30   9.203%   $99.7023   $99.70   $99.70   $99.70  
  Purchase #4 $239.62   6.258%   $254.6154   $254.62   $254.60   $254.60  
  Purchase #5 $14.25   3.156%   $14.6997   $14.70   $14.70   $14.70  
  Purchase #6 $219.86   6.768%   $234.7401   $234.74   $234.75   $234.70  
  Purchase #7 $140.85   11.682%   $157.3041   $157.30   $157.30   $157.30  
  7 purchase totals = $916.84       $995.3210   $995.32   $995.30   $995.30