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 $69.58   11.453%   $77.549   $77.55   $77.55   $77.50  
  Purchase #2 $31.51   3.462%   $32.6009   $32.60   $32.60   $32.60  
  Purchase #3 $239.64   13.418%   $271.7949   $271.79   $271.80   $271.80  
  Purchase #4 $75.37   9.342%   $82.4111   $82.41   $82.40   $82.40  
  Purchase #5 $95.32   13.144%   $107.8489   $107.85   $107.85   $107.80  
  Purchase #6 $147.87   13.621%   $168.0114   $168.01   $168.00   $168.00  
  Purchase #7 $232.98   5.371%   $245.4934   $245.49   $245.50   $245.50  
  7 purchase totals = $892.27       $985.7096   $985.70   $985.70   $985.60