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 $240.27   8.844%   $261.5195   $261.52   $261.50   $261.50  
  Purchase #2 $212.58   6.311%   $225.9959   $226.00   $226.00   $226.00  
  Purchase #3 $7.71   13.751%   $8.7702   $8.77   $8.75   $8.80  
  Purchase #4 $129.82   6.589%   $138.3738   $138.37   $138.35   $138.40  
  Purchase #5 $235.57   13.713%   $267.8737   $267.87   $267.85   $267.90  
  Purchase #6 $41.99   8.440%   $45.534   $45.53   $45.55   $45.50  
  Purchase #7 $60.73   13.724%   $69.0646   $69.06   $69.05   $69.10  
  7 purchase totals = $928.67       $1,017.1317   $1,017.12   $1,017.05   $1,017.20